SUMMARYSterigma and basidiospore development inCoprinus cinereusandBoletus rubinellushave been examined using an optical brightener and fluorescence microscopy. Development of the ellipsoid basidiospores ofC. cinereuswas associated with a characteristic series of fluorescence patterns: general, asymmetric, apical and finally subapical fluorescence. In the elongate spores ofB. rubinellus, after the initial asymmetric growth phase, fluorescence was consistently apical until the spore matured. Stage-specific fluorescence patterns were correlated with the changes in spore shape. Their significance is discussed.