We have examined the DNA obtained from 100 primary breast carcinomas for oncogene markers which might have predictive value for poor prognosis. Ninety-six of the tumors were analyzed for the presence of restriction fragment length polymorphisms (RFLPs) previously identified in the int-2 gene. An 8.4-kilobase BamHI fragment and a 3.9-kilobase PstI fragment specific for the int-2 gene, in the absence of other restriction fragments, was found in 17 of 50 (34%) lymph node-negative patients and in 27 of 44 (61%) lymph node-positive patients. This combination of int-2 RFLPs (8.4/3.9) was found in a significantly different proportion (P = 0.02) of patients with greater than 3 positive lymph nodes compared to patients with fewer positive lymph nodes, suggesting that these RFLPs may be valuable for distinguishing among node-negative patients for chemotherapy. In contrast, the observed low frequency of int-1, int-2, neu, and c-myc amplification limited their usefulness as clinical predictors of disease recurrence.