The kinetics of radiolabeled Ieucine, thymidine, uridine, and acetate uptake in the presence of 25 to 100 mg/100 ml halothane were studied with spinner cultures of HTC cells (Morris rat hepatoma 7288C) maintained in continuous logarithmic growth. At a time when exposure to halothane produces only slight reductions in DNA and protein synthesis and has no effect on RNA synthesis, a marked increase in lipid synthesis was detected. No preferential accumulation of activity was found in any of the neutral and phospholipid fractions examined, and the increases in the acid-soluble and acid-insoluble fractions were proportionate to the increase in total uptake of labeled acetate. Hence, it appears that the primary effect of halothane is the acceleration of transfer of acetate into hepatoma cells. Trifluoroacetate and trifluoroethanol, two proposed metabolites of halothane, had no effect on incorporation of the above-mentioned macromolecular precursors.