A pharmacokinetic approach was employed to design a dosing regimen for the i.v. use of procainamide (PA) which consisted of a loading infusion given over one hour followed by a maintenance infusion. Therapeutic serum concentrations of PA were achieved in less than 15 min, and toxic serum concentrations were avoided in 12 patients. A mean maximum serum concentration of PA of 5.78 mg/l was obtained with a loading infusion of 16.6 mg/min PA HCl. An average steady-state serum concentration of PA of 5.05 mg/l was obtained with a mean maintenance infusion of 222 mg/hour PA HCl. The total body clearance of PA in slow and fast acetylators averaged 31 and 43 l/h respectively. Use of PA in cardiac patients by i. v. infusion can be safe and effective therapy.