Acetaldehyde, the first metabolite of ethanol, mediates many of the biological effects of ethanol. We have previously shown that acetaldehyde, but not ethanol, stimulates collagen production in cultured human fibroblasts (Holt, K., Bennett, M., and Chojkier, M. (1984) Hepatology 4, 843-848). Here, we examined the effects of acetaldehyde on collagen gene expression. Confluent human fetal fibroblasts were incubated for up to 4 h in the presence of ascorbate (0.2 mM) alone or with the addition of either ethanol (12 mM) or acetaldehyde (200 microM). Acetaldehyde induced the production of collagen (up to 2.5-fold) and had a small inhibitory effect on procollagen secretion (-20%). The steady-state levels of mRNAs were measured by hybridizing total cellular RNA to specific cDNA probes at high stringency. Acetaldehyde increased the steady-state level of collagen alpha 1(I) and collagen alpha 2(I) mRNAs about 3-fold and had small effects on beta-actin mRNA (+50%) and collagenase mRNA (-50%). Northern blots revealed that the RNAs were intact and that acetaldehyde preferentially increased the abundance of the longer of the two collagen alpha 1(I) transcripts. Acetaldehyde increased both collagen alpha 1(I) and collagen alpha 1(III) transcriptional activity by 2.5-fold and had small effects on beta-actin and collagenase gene transcription. The increase in both collagen production and collagen mRNA levels induced by acetaldehyde was blocked by methylene blue, a scavenger of reducing equivalents. These data indicate that reducing equivalents, which enhance the formation and stability of acetaldehyde-protein adducts, may be required for acetaldehyde-stimulated collagen production. Thus, this study suggests that acetaldehyde increases collagen production by increasing collagen gene transcription in cultured human fibroblasts.