The glycosaminoglycan (GAG) distribution pattern of murine fetal tibiae cultured for 6 days in vitro was determined and the effects of drugs on the growth of the tibia explants in vitro, on their total GAG content and on their GAG distribution pattern were studied. The explants contained chondroitin-4-sulfate and chondroitin-6-sulfate in a relation of about 4:1; hyaluronic acid was not detected. During the incubation period of 6 days in vitro a mean increase in size of 47% and of the total GAG content of about 80-90% was observed; the GAG distribution pattern was practically unchanged. Incubation of the explants in a medium without ascorbic acid by contrast to a medium containing ascorbic acid (5 and 50 micrograms/ml) lead to a reduction of growth and total GAG content. The nonsteroidal antiphlogistic drugs phenylbutazone (20 and 200 micrograms/ml), ibuprofen (25 and 200 micrograms/ml) and alclofenac (25 and 400 micrograms/ml) effected a concentration dependent decrease of the growth and of the GAG content of the explants mainly due to a reduction of chondroitin-4-sulfate. Prednisolone (10 micrograms/ml) caused a significant increase of the GAG content of the explants leaving their GAG distribution pattern nearly unchanged. Aurothioglucose (400 micrograms/ml) induced a reduction of the growth and of the GAG content of the explants without altering the GAG distribution. Under low concentrations of Na-pentosanpolysulfate (5 micrograms/ml) an increase in growth and in the GAG content by a nearly unaltered GAG distribution pattern was observed, high concentrations (200 micrograms/ml), however, caused a reduction of growth and of the GAG content.