The testicular effects produced by di(2-ethylhexyl) phthalate (DEHP) in the rat, characterized by a decrease in the relative organ weight and histological changes in the seminiferous tubules, can also be produced by di-n-butyl, di-n-pentyl and di-n-hexyl phthalates. The corresponding monoesters of these compounds, formed in vivo as a result of the action of nonspecific esterases in the intestinal mucosa and other tissues, were equally effective in inducing testicular damage. Phthalate-induced testicular injury was accompanied by a decrease in the zinc content in the gonads and in increased urinary excretion of this element. Exposure of preparations of rat seminiferous tubule cells in culture to monophthalates capable of producing testicular injury resulted in a dose-related detachment of germinal cells from Sertoli cells in a manner similar to the effect seen in the intact animal. This in vitro system may find application in the elucidation of the toxic mechanisms involved in phthalate-induced testicular injury and in screening compounds likely to act in a manner similar to phthalates.