Chorionic villi from first trimester and term human placentas have been incubated in vitro and shown to release the lysosomal enzymes, beta-hexosaminidase, alpha-glucosidase and beta-glucuronidase. There was negligible release of the cytoplasmic enzyme, lactate dehydrogenase, under the same conditions. The first trimester villi released proportionally more of their lysosomal enzyme content than did the term villi. Extracellular levels of beta-hexosaminidase were raised and those of alpha-glucosidase and beta-glucuronidase were lowered when tissue was incubated with 1 microM colchicine, suggesting that microtubules are involved in the control of lysosomal enzyme release from placental villi.