Intraperitoneal administration of zinc chloride in vivo at 14 micrograms/g body weight (equivalent to 1/2 LD50) over a 3 week period induced an increase in liver weight. The mean weight of the livers in zinc-treated C57/6J mice was 50% higher than that of control animals. Image analysis revealed a concomitant and significant increase in the cross-sectional area and perimeter of the hepatocytes in the zinc-treated group. The mean cross-sectional area of hepatocytes in the zinc-treated mice was 337.2 +/- 4.3 microns2 as compared to 224.6 +/- 2.9 microns2 in the control group (p < 0.05, Mann-Whitney test). The mean perimeter of hepatocytes in zinc-treated mice was 72.4 +/- 0.5 micron as compared to 58.9 +/- 0.4 micron in control animals (p < 0.05). It would appear that subacute administration of zinc may result in increase in liver mass due to hypertrophy of the hepatocytes.