Studies were conducted on the effect of tricyclazole, a known inhibitor of pentaketide-derived melanin biosynthesis, on three Alternaria solani isolates. Accumulation of melanin shunt products occurred only in the presence of tricyclazole and varied with fungal strain, culture age, the growth medium, and light exposure. All A. solani strains accumulated 2-hydroxyjuglone (2-HJ) at all tricyclazole levels tested when grown on modified Czapek Dox agar, but on V-8 juice or potato dextrose agar only trace amounts of this product were found. As with Verticillium dahliae, which was included as a model, increasing tricyclazole concentrations resulted in progressively decreasing quantities of 2-HJ and increasing quantities of another shunt product, flaviolin. The quantities of flaviolin which accumulated in A. solani cultures were much smaller than in V. dahliae. On two media (amended Czapek Dox and potato dextrose agar) isolate 83W of A. solani produced high levels of altersolanol A. In the presence of tricyclazole, altersolanol A accumulation was reduced by 20–100% depending on inhibitor concentration, culture age, and light exposure. Altersolanol A and 2-HJ were both detected only after 8 days growth. Subsequently, their patterns of accumulation and disappearance from cultures were very similar. The observation that 2-HJ and flaviolin accumulate in tricyclazole-treated A. solani cultures supports the view that the melanin of these fungi is of a dihydroxynaphthalene and not a mixed polyketide-shikimate origin. The apparent inhibition of altersolanol A accumulation by tricyclazole is a separate phenomenon, not directly linked to inhibition of melanin biosynthesis, since 1,3,6,8-tetrahydroxynaphthalene, a key melanin precursor, cannot be an intermediate of altersolanol A biosynthesis.