Macromolecular contrast-enhanced functional CT was performed to characterize early perfusion changes in hepatocellular carcinoma (HCC). Fourteen rats with chemically induced primary liver tumors ranging pathologically from hyperplasia to HCC and 15 control rats were investigated. Two dynamic CT scans using an experimental macromolecular contrast agent were performed on a single slice 11 and 18 weeks after tumor induction followed by pathological examination. A deconvolution mathematical model was applied, yielding the hepatic perfusion index (HPI), mean transit time (MTT), liver distribution volume (LDV) and arterial, portal and total blood flows (FA, FP, FT). Analysis was performed on one slice per rat, containing overall two hyperplasia, six dysplasia and 15 HCC. On the first scans, HCC at an early pathological stage had a low FP (-30%, P=0.002) but a normal arterial-portal balance. On the scan contemporary to pathology, HCC perfusion parameters showed an inversion of the arterial-portal balance (HPI +212%, P<0.0001), with a high FA (+56%, P=0.002) and a low FP (-69%, P<0.0001). Sensitivity and specificity of detection of HCC by perfusion CT were high (87 and 80%) on late scans; but also on the earlier scans (86 and 65%), even though only one (7%) was visible to the eye. Perfusion-CT allowed early detection of HCC. This technique could contribute in the detection and characterization of liver lesions in clinical studies.