Human chorionic gonadotropin and alpha-fetoprotein are well established as serum markers for germ-cell tumors of the testis. Other protein markers of this disease are lactic acid dehydrogenase and placental alkaline phosphatase. There also are cytogenetic or chromosomal markers, particularly i(12p), and molecular markers in the form of oncogenes and tumor suppressor genes. Markers are valuable in diagnosis, staging, predicting tumor behavior, and monitoring therapy and disease recurrence.