This study set out to determine the relationship between splenic function (as assessed by the percentage of pitted red cells) and tuftsin activity, and to confirm the return of effective splenic function after splenectomy for trauma. Twenty-three patients (13 men) took part. Ten of mean age 48.5 (range 30-74) years had had the spleen removed for traumatic rupture and 13 of mean age 49.7 (range 23-66) years had undergone elective splenectomy. At the time of the study all patients had had the spleen removed a minimum of 1 year previously (mean 6.1 (range 1-15) years). Fifty healthy volunteers matched for sex and age were also studied. In each subject, residual splenic function was evaluated by counting the percentage of pitted red cells. Tuftsin activity was also determined. A highly significant negative correlation was found between pitted red cell percentage and tuftsin activity (rs = -0.80, P < 0.001). Compared with healthy controls (mean 21.6 (range 13-37) per cent), tuftsin activity was significantly reduced both in patients who had undergone splenectomy for trauma (mean 4.4 (range 0-9) per cent; P < 0.0001) and in those who had had elective splenectomy (mean 0; P < 0.0001). Tuftsin activity was significantly (P < 0.001) more depressed after elective than traumatic splenectomy. These data confirm a decrease in tuftsin activity following splenectomy and show that this deficit is significantly greater after elective than emergency removal. These observations confirm that residual splenic function is often present after traumatic splenectomy.