A prospective, randomized, controlled study was performed to determine the haematological and biochemical changes and clinical safety of postoperative autotransfusion (Solcotrans Orthopedic Plus system) in patients undergoing spinal surgery. Fifty patients were studied and were randomly allocated to Control (n = 25) and Solcotrans (n = 25) groups. Both groups had their postoperatively drained blood collected into the Solcotrans reservoir but only the Solcotrans group had this salvaged blood considered for reinfusion. After a 5-h postoperative collection period, analysis of the shed blood showed a haematocrit of 0.26 +/- 0.11, few platelets (80 +/- 63 10g.l-1), a fibrinogen level of less than 0.1 g.l-1 and a high level of D-dimers. The salvaged blood did not clot and aerobic and anaerobic culture produced no growth. The volume of blood collected was greater than 200 ml in 21 patients in the Solcotrans group who were autotransfused (384 +/- 101 ml, range 200-600 ml), and in 16 patients in the Control group. Within 15 min following completion of reinfusion of the salvaged blood there was a significant, but moderate decrease in platelet count (181 +/- 74 vs 223 +/- 90 10g.l-1, P < 0.001) and fibrinogen concentrations (2.1 +/- 0.8 vs 2.3 +/- 0.9 g.l-1, P < 0.02), and an increase in circulating D-dimers (P < 0.001) and plasma free haemoglobin concentrations (236 +/- 155 vs 82 +/- 79 mg.l-1, P < 0.001). Prothrombin time (PT) and activated partial thromboplastin time (APTT) did not increase, and potassium concentrations were not significantly affected.(ABSTRACT TRUNCATED AT 250 WORDS)