Potassium deficiency occurs in several conditions and is reported to cause muscle weakness and rhabdomyolysis. The mechanisms by which potassium deficiency cause muscle disease remain unknown, but the primary purpose of the present study was to determine whether abnormal muscle glycogen metabolism causes muscle weakness, as suggested by previous work. We monitored the natural history of potassium deficiency in two groups of dogs, one of which also received deoxycorticosterone acetate (DOCA), an agent commonly used in other studies to accelerate potassium loss. Group I dogs on potassium-free diet alone showed a 41% decrease in muscle potassium, no change in serum CO2, creatine kinase (CK), or muscle phosphorylase activity and only mild histopathologic abnormalities before death, after 198 +/- 42 days on the diet (mean +/- S.D.). In contrast, group II dogs on the same diet plus DOCA developed clinically similar severe weakness and died more rapidly than group I, 37 +/- 7 days (p less than 0.03). DOCA dogs showed a more rapid decrease in muscle potassium to the same level as group I, a 37% increase in serum CO2, an increase in serum CK to 1060 to 2775 IU/ml, a 23% decrease in muscle phosphorylase activity, and severe muscle histopathology, including rhabdomyolysis. Neither group showed any change in body weight, electromyogram (EMG), muscle glycogen concentration, glycogen synthetase activity, serum or muscle magnesium or phosphorus, or serum T3 or T4. In conclusion, dietary potassium deficiency in dogs causes severe weakness and death without causing rhabdomyolysis or abnormal muscle glycogen metabolism. Adding DOCA to the potassium-free diet creates a different model characterized by rapid clinical deterioration and rhabdomyolysis.