The formation of conidia in Phaeocytostroma ambiguum on different media and conditions was investigated in this study. Carnation leaf agar (CLA) and a 12 h photoperiod (24/18 degrees C) provided excellent conditions for the promotion of rapid formation of both alpha (alpha) and beta (beta) conidia in a number of P. ambiguum isolates. The dimensions of alpha- and beta-conidia amounted to 6.0-19.6 x 3.8-7.5 microm and 6.0-24.9 x 1.1-2.6 microm, respectively. They were produced on short or elongate, simple and branched conidiophores. beta-conidia have not been described before in P. ambiguum. Intermediate conidia were rarely found.