The effects of different gaseous regimes on the growth rate and extracellular enzyme location in vitro of colonies of Phlebia radiata, Phlebia rufa and Coriolus versicolor are reported. The two Phlebia species showed similar growth, extracellular enzyme and pH responses to gaseous composition (N2, O2 and CO2), but the responses of C. versicolor differed. Whilst maximum extension rates were obtained for all species under atmospheric gaseous composition, maximum biomass production occurred at 5% (v/v) O2 with 20% (v/v) CO2 for the Phlebia species and at 5% O2 with 60% CO2 for C. versicolor. The Phlebia species had a coenocytic margin (5–6 mm width) under atmospheric conditions, which increased in width with increasing percentage of CO2. Laccase and peroxidase activity were present throughout the septate region, but not in the coenocytic zone. With C. versicolor laccase and peroxidase activities appeared throughout the colony, but were more intense in the peripheral region, under all gaseous regimes. A laser densitometer, normally used to visualize proteins on electrophoresis strips, was used to estimate profiles of biomass and laccase-α-naphthol activity within colonies. Surface pH changed little in colonies of C. versicolor but dropped by over 1 pH unit from the margin inwards with the Phlebia species. The significance of these results is discussed in terms of ecological strategy and developmental versatility.