The generation of transgenic 'knock-out' mice which lack genes relevant to pain is becoming increasing common. However, only one visceral pain model, the writhing test, is available in mice. The aim of this study was to adapt cyclophosphamide cystitis, a model of inflammatory visceral pain described in rats, for use in mice, and to characterise its behavioural effects. The toxic metabolites of systemically-administered cyclophosphamide are excreted in the urine, and induce bladder inflammation. We compared the effects of cyclophosphamide (100 and 300 mg/kg i.p., 4 h survival period) and vehicle (saline) in male mice on spontaneous behaviour (4 h continuous video-tape, and a 5-min Open Field test after 4 h). Involvement of the urinary bladder and other abdominal tissues was assessed by macroscopic examination and measurement of Evan's Blue plasma extravasation. Cyclophosphamide (300 mg/kg) produced significant changes in behaviour, including 22 +/- 6 min of 'crises' of visceral pain-related behaviour and a 53% reduction in activity, and also induced haemorrhage and substantial plasma extravasation in the bladder, but no change in other abdominal tissues. We conclude that cyclophosphamide cystitis has many advantages as a model of sub-acute, inflammatory visceral pain in mice. It does not require surgery or intubation, and we have found it to produce consistent, reproducible and quantifiable behavioural changes, which are significantly correlated with the degree of bladder inflammation in the absence of inflammation of other abdominal tissues. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.