Synthetic aromatic analogs of retinoic acid were administered i.p. and p.o. to Fischer F344 rats bearing a transplantable chondrosarcoma. 35CO4 incorporation into glycosaminoglycans were compared for neoplastic and normal cartilage explants after removal from animals given various analogs. There was a direct relationship between [35S]glycosaminoglycan synthesis by chondrosarcoma chondrocytes and inhibition of tumor growth. The degree of inhibition of [35S]glycosaminoglycan synthesis in the neoplastic cartilage was dependent on the dose of the retinoid administered. At 20-mg/kg/day doses of retinoid for 4 weeks, 35SO4 incorporated into glycosaminoglycan by treated tumor explants was reduced as much as 95%. There was no reduction of [35S] glycosaminoglycan produced in normal costal cartilage of the same animals. Retinoid treatment of 20-mg/kg/day doses for 4 weeks resulted in a 75% reduction in glycosaminoglycan per mg of chondrosarcoma; there was no reduction in costal cartilage glycosaminoglycan. Retinoid (10- to 20-mg/kg/day doses) elevated collagen levels per mg of chondrosarcoma but had no effect on costal cartilage collagen. Combined in vitro and in vivo studies showed that retinoid administration modified neoplastic chondrocyte function but had no measurable effect on normal chondrocyte function.