The predictive value of a previously described Multivariate Prognostic Index (which incorporates weighted values of the mitotic activity index, tumor size, and the axillary lymph node status), and the nuclear DNA content (DNA) was evaluated in 156 patients with primary invasive ductal breast cancer, diagnosed between 1980 and 1983. The results were analysed with respect to the occurrence of distant recurrence and survival of the patients after at least 3 yr of follow-up (range 36-73 months; median 44 months). Known prognostic factors such as lymph node status, tumor size, and the mitotic activity index correlated independently with distant recurrence. Furthermore, in respect to survival, the investigated prognostic factors (except DNA content) were significantly correlated. The results indicate that the predictive value of the Multivariate Prognostic Index (MPI) is stronger (P less than 0.001) than of the nuclear DNA content (P less than 0.005) with respect to distant recurrence. In a Cox multivariate regression analysis DNA ploidy turned out to be an independent prognostic factor once the MPI was selected. Furthermore, in Cox's analysis, DNA ploidy was the fourth selected variable after lymph node status, mitotic activity index, and tumor size in individual parameter analysis. The results of this study indicate that, with respect to breast cancer screening programs, it seems worthwhile to integrate morphometric features, the MPI, and DNA ploidy in a new prognostic model.