Chondrocytes isolated from 16 day chicken embryo sterna and adult (18 month) bovine metacarpal-phalangeal joint cartilage were grown in monolayer culture for up to 5 days in the presence and absence of ascorbate (50ug/ml). RNA was isolated from these cultures and the steady-state levels of α1(I), α2(I) and α1(II) mRNAs were assayed using cloned DNA prohes encoding the respective procollagen mRNAs. Both ascorhate-treated and control chicken chondrocytes maintained the characteristic morphology and phenotype synthesizing the same levels of type II procollagen mRNA observed for sternal chondrocytes. The chicken chondrocytes., with or without ascorhate, did not synthesize increased levels of α1(I) or α2(I) mRNA. In contrast, when bovine articular chondrocytes were cultured with ascorbate. an increase in type II procollagen mRNA and, more interestingly, an increase in type I procollagen mRNA was observed during the 5 day culture period. Low levels of type I procollagen mRNA were detected in untreated chicken and bovine cultured chondrocytes and chicken chondrocytes isolated from sterna. These experiments suggest that when cultured in the presence of ascorbate under the conditions examined, chicken embryo chondrocytcs retain the differentiated phenotype unaffected by ascorbic acid while hovinc articular chondrocytcs begin to undergo a phenotypic change.