Many patients with chronic obstructive pulmonary disease (COPD) are symptom free when they receive an oral theophylline regimen. When these patients present to the emergency department with an acute exacerbation of their disease, the emergency physician faces a dilemma regarding appropriate therapy with IV aminophylline. The patient's serum theophylline level is unknown. A blind loading dose may result in inadequate treatment or iatrogenic toxicity. The Ames Seralyzer® is an immunoassay photometer that determines serum theophylline levels. We studied 90 patients with uncomplicated exacerbations of COPD treated in our ED before and after the installation of the Seralyzer®. Theophylline levels measured by the Seralyzer® had a high correlation with those measured by the hospital laboratory Abbott TDX (r = 0.914). Obtaining the theophylline level took a mean of only 0.46 hours with the Seralyzer®, compared with 2.13 hours with the hospital laboratory. The time from presentation to theophylline loading was 1.87 hours, compared with 3.28 hours with the hospital laboratory group, resulting in significantly greater relief of respiratory distress at three hours after arrival in the Seralyzer® group. The measured theophylline level was very poorly correlated with the physician's estimate of the level based on history (r = 0.353). We conclude that the Seralyzer® provided accurate assessment of levels, enabled earlier theophylline loading of patients and lessened delays, and decreased the probability of theophylline toxicity.