Griseofulvin caused concentration-dependent morphogenetic effects on the germination of macroconidia of Neurospora crassa. At 10–50 m, the germ tubes were typically sinuous. At 100–200 m, the compound induced multiple germ tube formation. Benomyl only slightly inhibited germination at low concentrations (0·25–0·5 m) and did not induce a sinuous pattern of germ tube elongation. It induced multipolar germination at 1–2 m. The analysis by DAPI fluorescence of the positioning of nuclei during germination revealed that benomyl, but not griseofulvin, prevented nuclear migration into multiple germ tubes. The aberrations of development induced by the two microtubule inhibitors were mediated without major changes in the N. crassa α- or β-tubulins.