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Mitotically active Schwann cells isolated from adult rat sciatic nerve segments were cultivated, using a bivariate BrdU/DNA flow cytometry analysis, to test the effect of b-FGF (10 ng/ml), α-MSH (10 ng/ml), NGF (10 ng/ml), PDGF-AB (10 ng/ml), and TGF-β1 (10 ng/ml) on the cell cycle. Compared to control or cholera toxin-treated cultures, no significant differences (P < 0.05; Newmann-Keuls test) were observed in the proportion of G0G1 cells, S cells, G2M cells, and in the LI when α-MSH, NGF, PDGF-AB, or TGF-β1 were present. The S phase duration varied from 6.16 ± 0.24 to 7.86 ± 2.6 h, and the deduced potential doubling time was estimated at between 46.70 ± 7.09 and 56.05 ± 7.55 h. In contrast, when b-FGF was added to the culture, the cell cycle was significantly modified, and the proportion of G0G1 cells decreased from 68-77% to 59-64%, while the proportion of S cells increased from 14-16% to 24.0-26.4%. Although S phase duration was not significantly changed (6.02 ± 0.36 h), the 1.7- to 2.8-fold LI increase reduced the potential doubling time to 25.99 ± 6.13 h. We conclude from these results that only b-FGF-induced adult rat Schwann cells dramatically reenter in cell cycle and that this growth factor may be an axonally derived signal-promoting mitogenesis after nerve injury. Copyright 1994, 1999 Academic Press