To the Editor: After we submitted our article, two other research groups, using multivariate analyses, reported on manic subtypes (1, 2; Cassidy et al., 2001). Surprisingly, all reports, including ours, proposed almost the same subtypings. Similarities and minor differences between the Duke study (Cassidy et al., 2001) and ours are summarized by Drs. Cassidy and Carroll. Their letter calls into question our conclusion that atypical manic features, such as aggression, psychosis, and depression, are likely to separately characterize several manic subtypes since "the factor scores have extremely large standard deviations, denoting a wide overlap of scores among the identified clusters." It should be noted, however, that standardized factor scores were used in our study. The mean factor score and its standard deviation were set at 0.0 and 1.0, respectively. As shown in Table 2 of our article, it is not true that the factor scores reported "have extremely large standard deviations." Our factors, called depressive mood and psychomotor/thought inhibition, have relatively large standard deviations in our mixed subtype. This reflects a large variance of these syndromes within this subgroup, suggesting the possibility that this subtype consists of several lower-order subgroups. It would be interesting to determine whether these lower-order subtypes are similar to the two mixed subtypes proposed by Dr. Cassidy et al. and whether the depressive inhibition factor identified in our study plays a role in describing these lower-order subtypes. Until these issues are clarified, it is too early to state that our "cluster analysis does not positively support Kraepelin’s subclassification of mixed states."