The distribution of antiarrhythmic drugs in human tissues may yield a better understanding of their therapeutic action and side effects. We report tissue distribution of flecainide in a patient who died suddenly while being treated chronically with the drug. Lungs showed the highest concentration of flecainide (143 micrograms g-1 wet tissue); liver, kidney and heart, in decreasing order, have good affinity for the drug. Flecainide was present also in the central nervous system in lower concentrations. The lowest concentration was found in the adipose tissue.