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A visual micromethod for measuring antifungal effects on germination and growth is described. The antifungal agent griseofulvin and the fungus Trichophyton mentagrophytes were used as materials to compare the micromethod with a standard assay based on dry mycelial weight. The micromethod was more sensitive than the weight method in detecting the minimum inhibitory concentration of griseofulvin (0.18 and 35 microgram/ml, respectively). At higher concentrations of griseofulvin (22.5 microgram/ml), the micromethod measured minimal fungal growth that was undetectable on a weight basis. The micromethod showed that griseofulvin does not change the number of spores forming germ tubes. Progressively severe alterations in fungal morphology occured as the concentration of griseofulvin was increased from 0.09 to 22.5 microgram/ml.