An anonymous drug questionnaire was administered to 2,256 men enlisted in the Army who were either entering or leaving Viet Nam. The percentage of respondents who reported flashbacks arising from the use, of "acid" (LSD and STP) was 23 percent; amphetamines, five percent; and marijuana, one percent. The majority of men attributing flashbacks to drugs other than acid had also used acid. No relationship was found between reports of flashbacks and frequency of acid use, exposure to a combat zone, or birth order.Abstract Teaser