Heroin continues to be one of the most serious drugs of addiction to treat. Newborn of heroin addicted mothers show symptoms of addiction. Evidence from animal experiments indicate that heroin causes changes at the cytological and biochemical levels. It has also been demonstrated that opiate receptors of nuclear fractions of nervous tissue bind opiate antagonists. Prolonged administration of "street heroin" to monkeys showed, in our preliminary studies, ultrastructural changes of the neuronal nucleus and nucleolus and a statistically significant level of chromosome aberrations in leucocyte cultures. "Street heroin" is composed of variable mixtures of heroin. The objective of these investigations is to study the effects of prolonged administration of pure heroin on the type, extent, persistence, and reversibility of CNS ultrastructural changes, and alterations of chromosomes in leucocytes, bone marrow and meiotic cells of both males and females. A group of pregnant monkeys will undergo sister chromatid exchange (SCE) and aberration analysis and then will be treated with pure heroin till delivery. Half of them and their newborn monkeys will be sacrificed. The other mothers and newborns will be allowed to "recover" from heroin for six months. This makes possible the evaluation of heroin's effects both on the mother and fetus. Another group of males and nonpregnant females will be treated in similar fashion for 24 months and half of these will be allowed to "recover" for six months. These experiments will furnish information on the prolonged effects and reversibility of the observed findings in chronic heroin addiction on primates. A fourth group of animals will serve as a control. After sacrifice of the animals, the ultrastructure of the CNS and chromosome analysis of bone marrow, testis and ovaries will be carried out. These experiments will yield information on the mode of action of chronic heroin addiction on the CNS, leucocytes, hemopoietic and reproductive cells in primates.