Many cancer cell lines were not growth inhibited by transforming growth factor (TGF)-β1. Human primary cells and human and mouse established cell lines were treated with TGF-β1 (5 ng/ml) for 48 hours. The cells were then pulsed for 2 hours with [3H]thymidine, and incorporated radioactivity was quantified. Results are presented as the average percentage of control (untreated cells) incorporation (± standard error) from three independent experiments with 6–12 replicates per experiment. The average percentage of control [3H]thymidine incorporation was calculated by dividing the average [3H]thymidine incorporation of TGF-β1-treated cells (from three independent experiments) by the average [3H]thymidine incorporation of nontreated cells (from three independent experiments) and then multiplying by 100%. Epid, epidermoid; Kid, kidney; Panc, pancreas; Pros, prostate.