With mycelium, arthrospores and microconidia of trichophyton mentagrophytes as inocula, a variety of in-vitro tests were used to assess the antifungal activity of the imidazoles; miconazole, clotrimazole, ketoconazole, econazole and tioconazole. For mycelial sensitivity, an agar plus method, a microtitre method using fragmented mycelial suspension and a turbidometric method were employed to determine fungistatic effects while a mycelial plug method indicated fungicidal activity. Spore susceptibility was determined by broth dilution and agar dilution methods for fungistatic action, while fungicidal activity was determined by measurement of rate of kill. The results obtained were affected to varying degrees by the test procedure, temperature and time of incubation, medium, pH and solvent. The spore forms were not more resistant than mycelium to the fungistatic effects of the imidazoles. There was little to choose between the various imidazoles in respect to their performance in these tests, with the exception of ketoconazole, which consistently gave higher MICs.