A total of 66 mechanosensitive units was recorded from an in vitro preparation of the chicken ureter with attached nerves. They were classified into three groups according to their functional properties. U-1 units (30% of the units) responded to contractions of the ureter and exhibited very low spontaneous activity (mean: 0.1 Hz). They had low average thresholds to distension (5.8 mmHg or 0.77 kPa), responded immediately to mechanical stimuli without exhibiting after discharges to strong stimuli. Their function might be the monitoring of peristalsis. U-2 units (38%) did not respond to contractions and had irregular spontaneous activities (mean: 0.7 Hz). They exhibited a high average activation threshold to distension (42.6 mmHg or 5.73 kPa) and after discharges to strong mechanical stimuli. U-2 units might be involved in nociception. U-G units (32%) were characterized by their long-latency response to any mechanical stimulus used and had a regular high ongoing activity (mean: 2.2 Hz). The pressure thresholds cover the whole range of the U-1 and U-2 units (5 to 70 mmHg or 0.67-9.33 kPa) with an average of 31.5 mmHg or 4.2 kPa. The peak discharge to pressure stimuli occurred much later than in the U-1 and U-2 units and they exhibited pronounced after discharges. Some U-G units were inhibited by mechanical stimuli. U-G units had large receptive fields sometimes covering the entire ureter. The units responded to electrical stimulation of the ureter after a variable latency, indicating that they were synaptically driven. In addition, a late long-lasting response to electrical stimulation was observed.(ABSTRACT TRUNCATED AT 250 WORDS)