Retrospective analysis of findings at double-phase helical computed tomography (CT) during arterial portography was performed in 42 hepatocellular carcinomas (HCCs) in 31 patients. Phase 1 scanning started 30-35 seconds after the beginning of injection of contrast material; phase 2 scanning started 10-18 seconds after the end of phase 1. The overall detection rate for HCCs was 83% (35 of 42) in phase 1, 81% (34 of 42) in phase 2, and 90% (38 of 42) for combined phase 1 and 2 findings.