The effect of certain methodological changes on the fit of the Wyer subjective probability model and the effect of belief change on cognitive structure were investigated. Using syllogistically-related proposition sets of the form "A,""If A then B,""If not A then B,""B," it was found that certain methodological improvements could increase the fit of the model above that obtained in previous research. Given a change in the subjective probability of "A," results indicated that the Wyer probability model predicted the observed change with reasonable accuracy. Changes in "A" beliefs tended to produce changes in related "B" beliefs but not in the conditional probabilities. In the case of a change in a "B" belief, however, there was no evidence of a corresponding change in the related "A" belief. (Author)