Serum tumor markers and patient allocation to good-risk and poor-risk clinical trials in patients with germ cell tumors. The allocation of patients with advanced germ cell tumors (GCT) to different treatment programs based on clinical characteristics is standard in the design of clinical trials today. Studies have shown that substantial differences exist between entry criteria and that these differences could influence the outcome of clinical trials. The factors contributing to these differences are not clear due to patient selection biases. Two hundred five unselected and consecutive patients allocated to and treated in good-risk and poor-risk treatment programs at Memorial Sloan-Kettering Cancer Center (MSKCC) were reassigned risk status by the Indiana University (IU) Classification. The results were compared with those of the Southeastern Cancer Study Group (SECSG). The results using both criteria indicated substantial agreement in total end results and the identification of good-risk patients. The results in poor-risk patients differed substantially, with 39 patients (19%) classified as poor-risk by MSKCC criteria and 66 (32%) by Indiana criteria. The major discrepancy occurred in IU Stage 7, in which 26 of 32 patients (81%) achieved a complete response. The major factor contributing to this difference in risk assignment was the use of serum tumor markers. Serum tumor markers must be incorporated into risk assignment criteria for GCT clinical trials to minimize the number of good-risk GCT patients in poor-risk trials. 