The aim the study was to define the relationships between a five-minute episode of mechanical colon distension (CD) of different degrees caused by the insertion of a balloon filled with 150 or 200 ml of water (CD 150 or CD 200) and neuroendocrine plasma levels (E, NE, DA, cortisol), as well as behavioural and clinical symptoms (reticulo-ruminal motility, heart rate, respiration frequency) as vegetative symptoms of nociceptive effects. Experiments were carried out on 12 female sheep, Polish merinos, in the anoestrus period. A five-minute episode of CD caused a highly repetitive, statistically significant increase in E, NE, DA, and cortisol plasma concentrations, as well as a reticulo-ruminal motility decrease (viscero-visceral inhibitory reflex) and nociceptive behavioural symptoms (looking around, defecation and/or urination, stretching, bleating). Practically all of these symptoms, which were easy to observe and quantify, recurred in animals suffering from colon distension, but their intensity was lower than in the case of e.g. duodenal distension. This suggests that this model of colic is less painful to animals. This less invasive in vivo method might be useful for the testing of analgesics and their antinociceptive effects in small ruminants.