Pulp cells from human permanent molars were isolated and established in culture; 40% showed positive alkaline phosphatase staining. When incubated with 50 micrograms/ml of ascorbic acid and 10 mM of beta-glycerophosphate, the cells formed a mineralized extracellular matrix; they could thus have the potential to differentiate into odontoblast-like cells in vitro. Collagen synthesis was analysed by SDS interrupted gel electrophoresis, Northern blot and slot blot: the cells produced predominantly (approximately 99%) type I collagen and only trace amount of type III collagen. The ratio of alpha 1 (I) to alpha 2(I) procollagen chains was about 68:32, indicating that no significant amount of collagen type I trimer was synthesized in this system. The ratios of alpha 1(I), alpha 2(I) and alpha 1(III) procollagen mRNAs were about 61:25:1; these were compatible with the ratios of corresponding procollagen alpha chains. In addition, a novel 5.8 kb pro alpha 1(III) mRNA was detected. These observations indicate that collagen synthesis in these cultured pulp cells was regulated at the transcriptional level.