Corneal fibroblast cultures were established from 3 normal and 4 keratoconus (KC) corneas. Type I collagen protein synthesis and steady-state RNAs were analyzed in these cultures by metabolic labeling studies, slot blots and immunofluorescent microscopy. Type I collagen proteins and steady-state RNAs were reduced in cells from 3 of the 4 KC cultures when compared with normal fibroblasts, suggesting that collagen expression is heterogenous in KC and that the heterogeneity is expressed at the cellular and molecular level. The type I collagen matrix synthesized by the KC fibroblasts appeared normal when analyzed by immunofluorescence, suggesting that the incorporation of type I collagen into the extracellular matrix is not affected in KC fibroblasts.