Clonogenic growth (defined as the formation of greater than or equal to 5 colonies per 5 x 10(5) viable nucleated cells per plate) of ovarian cancer specimens assessed in our clonogenic assay system was significantly associated with the proportion of tumor cells in the suspensions plated (N = 87; P = 0.0006), although there was no quantitative relationship with the corresponding plating efficiencies. An inverse correlation was observed between monocytes/macrophages/mesothelial cells (M) proportion and clonogenic growth (P = 0.013). These associations were most evident when only effusions were considered. Univariate analyses identified tumor cell content, M proportion and, to a lesser degree, granulocyte content as the only factors out of 12 examined to be correlated with colony formation. Multivariate analysis using a logistic regression model identified the proportion of tumor cells as the only significant factor predicting clonogenic growth in vitro (P = 0.0006). The overall accuracy of prediction for growth or non-growth was 63.2%.