In 60 below-knee amputations the healing of the stumps was correlated with the local skin perfusion pressure (SPP) measured preoperatively as the external pressure required to stop isotope washout using 131I- or 125I--antipyrine mixed with histamine. Of the eight cases with an SPP below 20 mmHg, no less than six (75 per cent) failed to heal and required reamputation at the above-knee level. Of the 12 cases with an SPP between 20 and 30 mmHg four cases (33 per cent) failed to heal but of the 40 cases with an SPP above 30 mmHg, there were only four cases (10 per cent) which did not heal. The difference in failure rate is highly significant (P less than 0.01). Four out of 30 diabetic patients required reamputation as against 10 out of 30 non-diabetics (0.05 less than P less than 0.10). The average SPP was higher in the diabetic group: 57 mmHg (range 18-93 mmHg) compared with 34 mmHg (range 8-68 mmHg) in the non-diabetic group (P less than 0.001). The postoperative SPP measured on the stumps was on average 8 mmHg higher than the preoperative SPP (P less than 0.001). The increase took place mainly in stumps with an SPP above 20 mmHg explaining why the preoperative SPP values related so closely to the postoperative clinical course. We conclude that a low SPP can be used to predict ischaemic wound complications, leading to reamputation at a higher level.