OBJECTIVE: To describe a patient with gastric retention of enteric-coated magnesium chloride tablets. Potential drug and disease etiologies accounting for failure to empty this dosage form are discussed. DESIGN: Single case report. CASE SUMMARY: A seriously ill patient with metastatic small-cell lung cancer accumulated 21 enteric-coated magnesium chloride tablets in his stomach during a four-day administration period. The patient had gastroscopic evidence of mild pylorospasm and suspected gastric motor dysfunction. The latter may have been the result of several factors including concurrent use of oxycodone, vagal dysfunction from chronic alcoholism and cisplatin-based chemotherapy, and possibly a paraneoplastic neuromuscular syndrome involving the gastrointestinal tract. CONCLUSIONS: Enteric-coated tablets are indigestible solids, often of considerable size. Strong antral contractions, associated with phase 3 of the interdigestive migrating myoelectric complex, are usually required to carry such dosage forms through a normal pyloric channel and into the duodenum. Seriously ill patients who may have gastric hypomotility or pyloric channel narrowing are probably not good candidates for therapy with large enteric-coated dosage forms.