Sporobolomyces spp. and Cryptococcus spp. colony size and spore germination of filamentous phylloplane fungi were studied in chamber fumigation experiments exposed to 0.05–0.2 p.p.m. SO2 for 24 h at 10 and 20°C. Lower temperature and higher SO2 concentration decreased the colony size of Sporobolomyces and Cryptococcus spp. Percentage spore germination of Alternaria alternata, Epicoccum nigrum and Fusarium culmorum was unaffected by SO2 concentration, although germ-tube extension markedly decreased. Both percentage spore germination and germ-tube length of Verticillium lecanii and Cladosporium herbarum were significantly reduced by 0.1 and 0.2 p.p.m. SO2, particularly at 20°.