Cevadine-induced changes in membrane potential, sodium transport, intracellular Na, K, and water content were investigated in sartorius muscles incubated in chloride-free (glutamate) Ringer. Cevadine sensitivity of muscles incubated in glutamate Ringer was about five times greater than that of muscles incubated in normal Ringer. Therefore, even 0.005 mmol/l cevadine could induce depolarization and membrane potential oscillations. The membrane potential oscillations were recorded much longer from muscles incubated in chloride-free Ringer (even in the 15th hour of treatment) than in normal Ringer. Depolarization and membrane potential oscillations reversed more slowly in cevadine-free glutamate Ringer than in alkaloid-free normal Ringer. The rhythmic activity could be recorded even in the 10th-15th hour of incubation in cevadine-free glutamate Ringer. Cevadine increased the 24Na uptake of muscles incubated in glutamate Ringer by an average of 230%. In comparison, the cevadine-induced increase of 24Na uptake of muscles incubated in normal Ringer was approximately 350%. In the presence of cevadine the 24Na loss of muscles incubated either in glutamate or in normal Ringer increased to the same degree, i.e. three times. The increase of 24Na loss developed faster in glutamate Ringer than in the presence of chloride. The water content of muscles incubated in cevadine containing, chloride-free (glutamate) Ringer did not increase significantly. Muscles incubated in normal Ringer with cevadine showed a 42.7% increase of water content in 2 hours. Intracellular Na content and Na concentration increased by about 60% during a 2-hour-treatment with cevadine in a chloride-free environment. At the same time, cevadine treatment increased the intracellular Na content and Na concentration of muscles incubated in normal Ringer by about 160% and 80%, respectively. The cevadine-induced decrease of intracellular K content and concentration of muscles incubated in glutamate Ringer was 5% and 10%, respectively, in 2 hours. On the other hand, the decrease of intracellular K concentration in muscles incubated in cevadine-containing normal Ringer occasionally reached 30% due to the increase of water content of the muscles. The cevadine-induced increase of the wet weight of muscles incubated in normal Ringer was practically irreversible. It was not possible to eliminate the increase of wet weight even by washout lasting for 10-15 hours.