The influence of IP 3 on Ca 2+ -, Na + ,K + -ATPase and basal Mg 2+ -ATPase activity of rat hepatocytes membranes was studied in control and after perfusion of liver by insulin-containing solution. It was established that in control, IP 3 increased specific activity of Ca 2+ -ATPase by (56 ± 13)% (Р < 0.05, n = 6) and basal Mg 2+ -ATPase by (52 ± 10)% (Р < 0.01, n = 6). After perfusion of liver with insulin-containing solution, it was found that application of IP 3 to membrane vesicules of hepatocytes caused only increase in basal Mg 2+ -ATPase activity by (68 ± 12)% (Р ≤ 0.01, n = 5). IP 3 did not cause changes in Na + ,K + -ATPase specific activity in control, or after liver perfusion by the insulin-containing solution. At the same time the perfusion of liver by the insulin-containing solution preveanted IP 3 -induced increase specific activity of Ca 2+ -ATPase and no effect on IP 3 -induced increase in the activity of basal Mg 2+ -ATPase. Keywords : IP 3 , ATPase activity, rat hepatocytes, insulin.