To the Editor: The study design employed by Ochs et al. in their article in the September 18 issue partly explains their negative findings. Previous studies by many groups1 2 3 have shown a definitive interaction between digoxin and quinidine, and the method used in most of these studies has been to increase doses until patients have steady-state digoxin levels, and then to introduce quinidine and study the effect. A similar study designed by Storstein et al.4 measured the changing clearance and serum elimination half-time in fully digitalized patients who were given quinidine. Peters et al.5 also studied fully digitalized patients, who.