Des-gamma-carboxy prothrombin (DCP) assay was performed by a staphylocoagulase method in 35 consecutive patients with small (less than 5 cm), resectable hepatocellular carcinoma (HCC). They also simultaneously received serum alpha-fetoprotein (AFP) assay. According to diagnostic strategy, patients were divided into two groups. Group I consisted of eight patients who were candidates for a mass screening project for HCC with elevated AFP levels (greater than 20 ng/ml). Five of these patients had an increased DCP level (greater than 6 U/l). Group II included 27 victims of chronic hepatitis B or cirrhosis whose tumors were detected by ultrasonography during regular follow-up. In this group, increased DCP and AFP levels were observed in 11 and 16 cases, respectively. Of 14 patients with smaller HCC (less than 3 cm), only three had elevated DCP levels, while eight patients had an abnormal AFP level. When these two assays were combined, 18 of 27 patients in group II and nine of 14 patients with smaller HCC (less than 3 cm) revealed elevation of one or both of the two markers. A total of 16 out of 35 patients with small HCC had abnormal DCP levels. In conclusion, DCP assay is less sensitive than AFP assay in the detection of small HCC, and the combination of both markers has little complementary effect.