Carbon tetrachloride (CCl4) biotransformation and covalent binding was measured in 1000g liver fractions by determining the amount of CCl4 metabolites covalently bound to proteins and lipids at various (5-60 min) incubation times. Reactive intermediate binding to proteins and phospholipids peaked at 20 min, whereas CCl4 metabolites associated with neutral lipids (primarily diacylglycerol) were initially low (0-15 min) and then gradually increased from 20-60 min. The rise in labeled diacylglycerol was associated with a decrease in phospholipids containing covalently bound CCl4 metabolites, since CCl4 bioactivation increased phospholipase C (PLC) activity three- to fourfold. In contrast, when CCl4 bioactivation is absent, 0.5mm CCl4 has little effect on PLC activity. PLC activation by high doses of CCl4 occurs by bioactivation-independent mechanisms. Therefore, there are two components of CCl4-induced PLC activation. Under both conditions, the activation of PLC may be a key event in CCl4 hepatotoxicity since PLC disrupts the functional and structural integrity of membranes by degrading membrane phospholipids. (Copyright (c) 1988 Academic Press, Inc.)