Hemihepatic portal vein embolization (PVE) concomitantly induces atrophy in embolized and compensatory hypertrophy in nonembolized hepatic lobes. The aim of the present study was to evaluate the involvement of growth stimulatory and inhibitory factors in these hepatic lobes after PVE. Liver specimens from the embolized and nonembolized lobes of ten patients who underwent hepatectomy (8–22 days) after undergoing PVE were obtained. Proliferation and apoptosis were examined immunohistochemically using Ki-67 and the Tdt-mediated dUTP-biotin nick end-labeling method. The expression of transforming growth factor-α (TGF-α) and transforming growth factor-β (TGF-β) was also examined by immunohistochemical staining. PVE induced hepatocyte apoptosis in the embolized lobe and hepatocyte proliferation in the nonembolized lobe. TGF-α expression in the hepatocytes of the nonembolized lobe was markedly increased, whereas TGF-α was also overexpressed, albeit moderately, in the embolized lobe. In contrast, TGF-β expression in the hepatocytes of the embolized lobe was significantly increased, and TGF-β expression was also increased, although to a lesser extent, in the nonembolized lobe. The degree of volume changes of the nonembolized lobe and the embolized lobe after PVE was statistically correlated with the ratios of TGF-α and TGF-β expression in these lobes (r = 0.886, P < .0001). In conclusion, these findings indicate that TGF-α and TGF-β expression (assessed by immunohistochemical staining) increase in relation to hepatocyte proliferation and apoptosis, respectively, after PVE in humans and the balance of the two factors may contribute to hepatic atrophy and hypertrophy concomitantly observed in this model.