A 10-year prospective study of cases of suspected necrotising fasciitis was made, involving 53 patients. Of these, 28 had histologically proven necrotising fasciitis, 25 did not. Serum lactate measured at presentation of those who had the condition was 4.1+or-1.62 mmol/l and roughly half of that in those without necrotising fasciitis (p<0.0001). The urgency with which excision must be undertaken in cases of this disease, makes any assistance with the difficult diagnosis in the early stages very welcome. Judging by this paper, serum lactate levels could be very helpful in making an early decision.