DNA analysis of multiple synchronous renal cell carcinomas. The authors used retrospective quantitative DNA analysis to study interrelationships between multiple synchronous renal cell carcinomas in seven patients. DNA content was determined by image analysis on Feulgen-stained nuclear smears prepared from multiple paraffin blocks from each tumor. Tumors were unilateral in four cases and bilateral in three. Ten tumors had homogeneous, and four heterogeneous DNA stemlines. Intertumoral heterogeneity in four cases suggested multifocal origin. Identical DNA aneuploid indices in bilateral tumors in one case suggested metastasis from a solitary origin. Abnormal DNA content and heterogeneous populations began to appear in the size range 2.0 to 5.0 cm. All tumors over 5.0 cm contained nondiploid populations. Although the interrelationships between these multiple synchronous neoplasms are not entirely clear, the DNA analysis suggests that the occurrence of nondiploid stemlines and heterogeneous DNA content may parallel both tumor growth and more aggressive behavior. 