Hepatic masses showing higher density than that of liver after 3 min (prolonged enhancement) and/or having prominent enhancement after the arterial-dominant phase (delayed enhancement) of dynamic CT (bolus enhancement followed by serial scans) were reviewed. Prolonged enhancement was noted in any hepatic masses, but mainly in cavernous hemangioma and capsule of hepatocellular carcinoma, whereas delayed enhancement occurred in capsule of hepatocellular carcinoma and occasionally in metastatic tumor. The volume of arterial and portal blood supply, turnover rate of blood, extent of the interstitial space, and diffusion rate between the vascular and interstitial space, as well as dose and speed of contrast agent administered, seemed to be important factors in such contrast enhancement. Prolonged enhancement and delayed enhancement are nonspecific but still are of some value in the differentiation of hepatic masses on dynamic CT.