We have treated six patients with theophylline overdoses, all of whom had high blood theophylline levels but lacked symptoms of serious toxicity. All improved with conservative therapy. While other reports of theophylline overdose describe aggressive therapy in patients with high blood levels and serious toxic signs, we believe blood levels cannot be used to predict serious toxic reactions. The symptoms that precede toxic convulsions--excitation, irritability, twitching, and alertness--are more valuable than blood medication levels as indicators of the need for aggressive therapy.