An outbreak of hyoscine hydrobromide toxicity was detected through the Australian pharmacovigilance system. The unexpectedly wide variation in hyoscine hydrobromide content between individual tablets within single packets created difficulties in initially explaining the clinical experiences. Strict time requirements for review of incoming adverse drug reaction reports and close involvement of the highly skilled national drug regulatory laboratory resulted in early identification of the cause of the outbreak and led in turn to the identification of malpractice by the contract manufacturer.