Abstract Patients with decreased renal function have a very high incidence of cardiac disease and stroke and have very high levels of plasma homocysteine. We have shown that plasma S-adenosylhomocysteine is a more sensitive indicator of the risk for cardiovascular disease than is plasma homocysteine. We measured plasma S-adenosylhomocysteine and total homocysteine in 36 patients with renal insufficiency and in 17 control subjects. The mean (± SD) value of S-adenosylhomocysteine for renal patients was 90.4 ± 49.4 nmol/L, and the corresponding value for control subjects was 25.8 ± 6.0 nmol/L. The mean value of homocysteine for renal patients was 20.9 ± 7.2 μmol/L, and the corresponding value for control subjects was 10.9 ± 2.7 μmol/L. For S-adenosylhomocysteine, the values of four patients overlapped those of control subjects, whereas for homocysteine 10 patient values overlapped control values. S-adenosylhomocysteine is a more sensitive indicator than homocysteine for renal disease (89% v 72%, respectively, P = 0.034).