We studied the size of the liver graft and the host liver in six consecutive patients undergoing auxiliary heterotopic liver transplantation for chronic end-stage liver disease. In all cases, a liver reduced in size by left lateral hepatectomy was inserted. The sizes of the graft and host liver were estimated by planimetry of two-dimensional di-isopropyl iminodiacetic acid scintigrams taken 3, 7, 21, 90 and 180 days after surgery. Graft size increased from a mean of 12.2 cm2 (95% confidence interval = 10.2 to 14.1) on day 3 to a maximum of 14.8 cm2 (95% confidence interval = 13.4 to 16.1) on day 21 and remained stable thereafter; in contrast, the host liver decreased in size from 9.6 cm2 (95% confidence interval = 6.8 to 12.3) on day 3 to 3.9 cm2 (95% confidence interval = 3.0 to 4.8) at mo 6. We conclude that in patients with chronic liver failure, an auxiliary allograft reduced in size and placed adjacent to the host liver shows regenerative growth within 3 wk, whereas the host liver atrophies in 3 to 6 mo.