Karlis' first research, conducted in the 1940s, was inspired by the work of William Fletcher Barrett, specifically his book, Death Bed Visions. In an attempt to build on Barrett's research, he and Erlendur Haraldsson conducted a four year study whereby they sent out hundreds of questionnaires to doctors and nurses in both the US and northern India, asking them about their observations regarding dying patients. The results, covering 50,000 patients, showed that a large proportion reported their adult patients seeing visions just before death.
Their research highlighted differences between cultural experiences near death. They found that a person's religion greatly influenced what was seen and that this was most apparent when observing the differences between Indian and American experience where Indian patients were far more likely to see a personification of death than Americans.
He repeated this experiment again in 1976, this time investigating the effects high fevers, painkillers and diseases which specifically affect the brain, had on a patients reported experiences at the time of death. Despite the far smaller pool of data (the newer study involved just 877 doctors in the USA alone), Osis concluded to his satisfaction that what he called the "sick brain hypothesis" – that the decrease of brain activity was causally linked to near death experiences – did not stand up to scrutiny.
On being asked about the practical applications of his theories, Osis remarked that "One definite finding of the research is the diminishing fear of death".
In 1957, Osis became the director of the Parapsychology Foundation in New York, being elected as president in 1961. In 1962, he began working with the American Society for Psychical Research, work which continued for many years. In 1971, he and Haraldsson co-authored the book At the Hour of Death, describing the results of their research.
The method Osis used to collect data has drawn criticism from the scientific community. Terence Hines wrote:
Osis and Haraldsson’s (1977) study was based on replies received from ten thousand questionnaires sent to doctors and nurses in the United States and India. Only 6.4 percent were returned. Since it was the doctors and nurses who were giving the reports, not the patients who had, presumably, actually had the experience, the reports were secondhand. This means they had passed through two highly fallible and constructive human memory systems (the doctor’s or nurse’s and the actual patient’s) before reaching Osis and Haraldsson.
- Haraldsson, Erlendur PhD & Osis, Karlis PhD: At the Hour of Death. Hastings House / Daytrips Publishers; 3RD edition, 263 pp. ISBN 0-8038-9386-8
- "Osis, Karlis [1917–1997]". The Element Encyclopedia of the Psychic World 1. Harper Element. 2006. pp. 505–506.
- Wilson, Colin (December 28, 2006). "Ghosts of the Tsunami; Spectres on the beach. Voices calling from empty buildings. On the second anniversary of the tsunami, the extraordinary story of how one British couple set out to bring peace to the victims' spirits". Daily Mail. p. 54.
- Reitman, Valerie (July 4, 2004). "When dying plan for earthly journeys: People who experience 'nearing death awareness' say they are going on a trip or trying to finish something". Calgary Herald. pp. B5.
- Menz, Robert L. (Winter 1984). "The Denial of Death and the Out-of-the-Body Experience". Journal of Religion and Health (Springer) 23 (4): 326. JSTOR http://www.jstor.org/stable/27505797.
- Woodward, Kenneth L. (July 12, 1976). "Life After Death?". Newsweek. p. 41.
- "Near-death Experiences Illuminate Dying Itself". New York Times. October 28, 1986. p. 8.
- "Paid Notice: Deaths Osis, Dr. Karlis". The New York Times. December 29, 1997. pp. Section B, Page 8.
- Monaghan, Charles (November 9, 1986). The Washington Post. pp. X23.
- Terence Hines. (2003). Pseudoscience and the Paranormal. Prometheus Books. p. 102
- The New Paranatural Paradigm: Claims of Communicating with the Dead by Paul Kurtz