Values are means ± SEM from 12 individual determinations. *p < 0.01 (one-way ANOVA + Fisher PLSD), if compared with control astrocytes. TGFβ1- or TGFβ2-like activity was determined by measuring the ability of the medium to reduce [³H]thymidine incorporation in mink lung epithelial cells. One arbitrary unit corresponds to the antiproliferative activity produced by 5 pg/ml of authentic human TGFβ1 or -β2. Values were calculated from reference curves constructed with authentic human TGFβ1 and -β2 (from 0.1 to 10,000 pg/ml). Maximal concentrations of TGFβ1 or -β2 (300–1000 pg/ml in different assays) reduced [³H]thymidine incorporation by 70–80%. The different numbers between TGFβ1- and TGFβ2-like activities reflect the slightly different potency we have found between authentic TGFβ1 and -β2 in reducing [³H]thymidine incorporation. bFGF failed to reduce [³H]thymidine incorporation in mink lung epithelial cells [[³H]thymidine incorporation (cpm/well): basal = 28840 ± 1737; TGFβ1, 300 pg/ml = 6900 ± 2349; bFGF, 3 ng/ml = 34560 ± 4510;n = 4].