The effect of gamma interferon on the simulated granuloma formation induced by the eggs of Schistosoma mansoni was observed using a model of SEA-polyacrylamide beads and mouse spleen cells in vitro. The results showed that interferon at the concentration of 0.1~10U/ml could not affect significantly the granulomatous response of the spleen cells of unimmunized mice (Table 1); but at the concentration of 10-100U/ml it could inhibit significantly the response of the spleen cells of immunized mice (Table 2). The mechanism of the inhibition is probably due to the suppression of T helpers in the present study.