Cyclobenzaprine (CBP) has a cyclic structure similar to amitriptyline. In overdose, CBP has been suggested to produce the cardiovascular and neurologic toxicity found with the cyclic antidepressants. To examine this possibility, a retrospective chart review of all cases of CBP exposure reported to five regional poison centers was performed for the years 1989-93. There were a total of 750 charts identified for CBP exposure, of which 523 had data sufficient for evaluation. There were 121 polydrug ingestions leaving 402 pure CBP ingestions. Ages ranged from 7 mo to 77 yrs, with a mean of 20 yrs; 26% were 6 yrs or less. Females comprised 63% of the patient group. No deaths occurred. Dysrhythmias beyond sinus tachycardia were infrequent, and none were life-threatening. No seizures occurred. Common effects were lethargy, sinus tachycardia, and agitation, and both hypertension and hypotension were seen. All symptomatic cases with a known time of ingestion were symptomatic within 4 h of ingestion. Doses ingested ranged from 5-1000 mg, with a mean of 133 mg. Asymptomatic and symptomatic patients had a mean dose ingested of 45 mg and 183 mg, respectively. Treatment was primarily gastrointestinal (GI) decontamination and supportive care. Other therapies required were mechanical ventilation, dopamine, fluid bolus, sedation, and foley catheter. Symptoms requiring treatment beyond GI decontamination did not occur with ingestions less than 100 mg. In conclusion, cyclobenzaprine does not appear to produce the life-threatening cardiovascular or neurologic effects of the cyclic antidepressants in doses less than 1 g. Lethargy and anticholinergic effects are prominent, though serious toxicity is infrequent.