OBJECTIVE: The objective was to determine the efficacy of CA 15-3 as a complimentary marker to CA 125 for ovarian cancer screening. STUDY DESIGN: Serum CA 125 and CA 15-3 levels were measured by immunoradiometric asaay in 550 apparently healthy women and 46 ovarian cancer. RESULTS: The cut-off level of serurn CA 125 in the apparently healthy women were 65.0 U/ml in the under 50 age group and 34.8 U/ml in the over 50 age group, And the cut-off level of serum CA 15-3 were 37.0 U/ml and 34.7 U/ml, respectively. The sensitivity of serum CA 125 were 95.7% at the cut-off level of 35 U/ml and 93.5% at the cut-off level of 65 U/ml. And that of serum CA15-3 were 52.2% at the cut off level of 30 U/ml and 45.7% at the cut off level of 40 U/ml. The specificity of serum CA 125 were 95.6%(35 U/ml) and 99.3 %(65 U/ml). And that of serum CA 15-3 were 98.3(30 U/ml) and 99.6%(40 U/ml). CONCLUSION: The serum CA 15-3 assay combination with CA 125 would not contribute to increase the efficacy of screening strategy for ovarian cancer. The serum CA 125 is very useful tumor marker in ovrian cancer screening, especially in the over 50 age group and at 35 U/ml cut-off level.