Most sexual activity among homeless adolescents is unsafe sex, that is, without the protection of condoms, and their relationships, either heterosexual or homosexual, change frequently. The pregnancy rate among homeless girls is high; a study of 16- to 19-year-old girls in 19 cities found that 31 percent among the homeless sample were pregnant compared to 9 percent of the control sample. Homeless adolescents use intravenous (IV) drugs much more than do other adolescents; those who do not may place themselves at risk anyway by engaging in sexual relations with those who do. Relatively few adolescents have been reported as having AIDS as the latency period of the virus averages eight years and therefore tends to show up only after adolescence. Homeless adolescents face extraordinary barriers to services available to other adolescents. In turn, service agencies find their needs difficult to serve because of their tendency to distrust adults. 47 references (Author abstract modified)