To verify the frequency and severity of metabolic abnormalities occurring as a result of intentional theophylline overdose, we retrospectively analyzed admission laboratory data from 22 cases of theophylline poisoning. Hypokalemia, hyperglycemia, and leukocytosis were frequent findings, and the magnitude of these abnormalities was related to the corresponding serum theophylline level. Although measurements were available for a smaller number of patients, respiratory alkalosis, hypophosphatemia, and hypomagnesemia were also common findings. Given the potential contribution of these abnormalities to the cardiovascular and neurologic toxicities of theophylline, it is important that their presence in patients with overdose be anticipated.