This paper reviews recent studies of rational emotive, therapy (RET) to determine whether there is empirical evidence to support the assertion that the reasons for therapeutic gains in RET are via changing irrational to rational beliefs. Before such issues can be examined, problems with the definition and measurement of irrational beliefs are first discussed and the evidence pertaining to the validity of current measures is addressed. Treatment outcome studies using RET published between 1982 and 1988 were examined. While RET has been shown to be relatively efficacious, no evidence was found to support the assertion that the mechanism for the efficacy of RFT is via change of irrational beliefs to rational beliefs.