Seven North American moss species responded differentially to fumigations with sulfur dioxide ranging from 0.5 to 4.0 ppm. Leucobryum glaucum and Dicranum scoparium were the most sensitive species; Dicranella heterophylla, Polytrichum ohioense and Pottia truncata, the most resistant. The results of fumigations with 0.1 to 4.0 ppm sulfur dioxide for 8 hours on cultured gametophytes of Polytrichum ohioense indicate that protonema and young gametophores are substantially more sensitive to sulfur dioxide than mature gametophores. Protonema were killed at concentrations of 0.2 ppm sulfur dioxide; whereas mature gametophores were resistant to sulfur dioxide at concentrations of 2.0 to 4.0 ppm. These data suggest that the observed moss impoverished zones around sulfur dioxide sources may result from the blocking of moss reproduction rather than direct effects on mature plants.