Adequate aeration of cultures was shown to be essential for basidium formation in isolates of several species belonging in the Ceratobasidiaceae. Moreover, fruiting was strongly influenced by the physical characteristics of three commercially available brands of petri dish that differed in their capacity to permit atmospheric exchange between the interior of the dish and the external environment. Dextrose-yeast extract agar, on which fungi were grown before transferring to sporulation media, was found to be a suitable primary substrate for eight of 10 species tested but basidium formation in most isolates was critically affected by the composition of the sporulation medium and by the volume of incculum transferred. The significance of these findings is considered in relation to the potential of existing methods to give reproducible leve!s of basidium fcrmation in different laboratories.