An experiment was conducted to test three hypotheses concerning effects of social uncertainty and general trust on commitment formation, hypotheses derived from Yamagishi & Yamagishi's (1994) theory of trust. First two hypotheses were supported, while the last one was not. First, increasing social uncertainty facilitated commitment formation. Second, low general trusters formed mutually committed relations more often than did high trusters. Finally, the prediction that the effect of general trust on commitment formation would be stronger in the high uncertainty condition than in the low uncertainty condition was not supported. Theoretical implications of these findings for the theory of trust advanced by Yamagishi and his associates are discussed.