Digoxin-like immunoreactive substance(s) (DLIS) in the sera of patients with renal insufficiency may confound attempts to monitor serum digoxin levels. We investigated whether DLIS would affect the radioimmunoassay (RIA) for digitoxin. DLIS was detected by RIA in 9 of 38 chronic hemodialysis patients and in none of 25 healthy controls. Digitoxin levels were not elevated in either the control or dialysis group, and false-positive results for digitoxin by RIA were not obtained in any patient with DLIS. It is concluded that DLIS does not interfere with the digitoxin RIA, nor are digitoxin levels spuriously elevated in chronic hemodialysis patients. Digitoxin may be a preferable preparation for digitalis-dependent dialysis patients with DLIS.