Using a Clark oxygen electrode and a ¹³³Xe clearance technique, tissue oxygen tension (T_o2) and blood flow have been determined in the small and large bowel of a rabbit experimental model. The predictive value of perianastomotic T_o2 in colonic anastomoses was determined, healing being assessed by leakage rate, tensile strength and hydroxyproline content. The effect of suture technique on colonic perianastomotic T_o2 has also been studied. Colonic and small intestinal T_o2 correlated with blood flow (r = 0·93). Basal colonic blood flow and oxygen tension were significantly lower than in the small intestine (P<0·01). Interrupted and continuous suture techniques decreased colonic perianastomotic T_o2, although mean T_o2 in the continuous group was significantly lower than in the interrupted group (P<0·01). The leakage rate was 10 per cent (1/10) for anastomoses constructed with a perianastomotic T_o2 above 55 mmHg compared with 100 per cent (10/10) if less than 25 mmHg (P<0·001). Perianastomotic T_o2 correlated with breaking energy (P<0·001), breaking strength (P<0·01) and hydroxyproline content (P<0·05).