The bioavailability of digoxin from 3 silica matrix formulations was assessed in single-dose crossover studies in 12 healthy human volunteers: digoxin/silica matrix tablets (I, Digacin), digoxin/silica matrix in capsule form (II) and digoxin/silica matrix dragées, protected against gastrict juice by film coating (III). Urinary glycoside excretion for 6 days after 0.5 mg doses were measured by radioimmunoasay. Referring to an intravenous injection the bioavailability of digoxin from Digacin tablets is 82%, from the encapsulated matrix 69%, and from the dragées 54%. In comparison with corresponding results from other investigators Digacin tablets havet the same high bioavailability as digoxin solutions. In vitro liberations of digoxin from the silica matrix formulations (94% in 90 s) is significantly better than from conventional tablets produces from a digoxin-lactose trituration (61% in 90 s).