We have measured the activity S-adenosyl-L-methio-nine synthetase in liver biopsies from a group of controls (n = 17) and in 26 cirrhotics (12 alcoholic and 14 posthepatitic). The activity of this enzyme was markedly reduced in the group of cirrhotics (285 ± 32 pmoles per min per mg protein) when compared with that observed in controls (505 ± 37 pmoles per min per mg protein). No differences in S-adenosyl-L-methionine synthetase was observed between both groups of cirrhotics. Similarly, a marked reduction in the activity phospholipid methyltransferase was also observed in liver biopsies from the same group of cirrhotics (105 ± 12 pmoles per min per mg protein) when compared with the control subjects (241 ± 13 pmoles per min per mg protein). Again, no difference in the activity of this enzyme was observed between both groups of cirrhotics. These results indicated a marked deficiency in the metabolism of S-adenosyl-L-methionine in cirrhosis.