Differences in morphological changes of basophils between antigen and anti-IgE　stimulation were examined in atopic subjects in relation to histamine release.　1. Antigen-　induced release of histamine was remarkably more rapid and larger at any incubation time than the release by anit-IgE, and a significant difference was found at 3 to 9 min. 2. Decrease in number of basophils induced by antigen was significantly higher for 12 to 15 min incubation time than that by anti-IgE. 3. Morphological changes of basophils representing increased motility such as an increased ratio of short to long axis diameter (L/S ratio) and an increased incidence of basophils with localized granules (LG) were more often observed in antigen stimulation compared with anti-IgE, and the L/S ratio of the cells was significantly more increased in antigen stimulation at 6 and 15 min. 4. There was no difference in morphological changes of basophils showimg swollen type (degranulation) such as an increased mean diameter (MD) of the cells between antigen and anti-IgE. These results suggest that antigen activates basophils and induces increased motility more strongly than anti-IgE, but the action on degranulation was not different between the two agents.