Enhanced production of collagen is central to fibrotic disorders such as hepatic cirrhosis and pulmonary fibrosis. We describe a sensitive, quantitative, and high-throughput technique for measuring hepatic collagen synthesis in vivo through metabolic labeling with heavy water (²H₂O). Rats and mice received ²H₂O in drinking water for up to 35 days. Deuterium incorporation into collagen-bound amino acids (AA) alanine and hydroxyproline (OHP) was measured by gas chromatography-mass spectrometry. A threefold stimulation of collagen fractional synthesis was observed under the maximum dosage of carbon tetrachloride (CCl₄; 1.67 ml/kg). Deuterium enrichment was systematically 20% higher in AA from monomeric collagen relative to dimeric collagen, consistent with slower turnover of the latter. Administration of 1% griseofulvin to mice resulted in a significant, threefold increase in liver collagen synthesis, observable within 12 days and consistent with predicted interstrain differences (C57/Bl6J > BALB/c). Deuterium enrichments of OHP from total liver proteins correlated well with alanine or OHP from isolated collagen. Fibrogenesis subsided after withdrawal of CCl₄ exposure and was reduced to various degrees by coadministration of interferon-γ, rosiglitazone, atorvastatin, or enalapril. Changes in isotopically measured collagen synthesis correlated with, but were more sensitive and reproducible than, standard histological staining (trichrome) for fibrosis. In summary, liver collagen synthesis can be measured sensitively and with high precision over a short time period, without radioactivity, thereby providing a relatively high-throughput in vivo strategy for rapidly measuring profibrotic activities of suspected hepatotoxicants and antifibrotic activities of drug candidates.