SUMMARY: A system for the rapid and relatively synchronous germination of conidia from a clinical isolate of Aspergillus fumigatus is described. The polyene-mediated release of K+ from germinating conidia has been determined. Ungerminated conidia were insensitive to amphotericin B methyl ester (AME) at concentrations > 50 μg/ml, but rapidly became sensitive to 1 to 2 μg AME/ml during the initial stages of germination. These findings have been correlated with minimum inhibitory concentration values obtained in studies of conidial germination and hyphal outgrowth using a variety of growth tests.