Many nursing women returning to a full-time job and desiring to continue to breast feed are using oxytocin nasal sprays to facilitate breast emptying during the work day. Very few complications have been reported from its use, and the preparation has been assumed to be innocuous. However, we encountered a nursing mother whose life appears to have been jeopardized by the excessive and unmonitored application of such a spray. The patient was hospitalized for a viral illness and given a large quantity of intravenous fluid. In association with excessive self-administration of an oxytocin nasal spray, she developed severe water intoxication, with hyponatremic encephalopathy and convulsions. During the same hospitalization the patient subsequently developed a Guillain-Barré type of peripheral polyneuritis. The syndrome of inappropriate secretion of antidiuretic hormone has been reported to accompany the neurologic manifestations of the Guillain-Barré syndrome and may have been the cause of the convulsions. However, the temporal associations in this case strongly favor the unmonitored use of the oxytocin nasal spray as etiologic.