We evaluated the surgical results of the modified Blalock-Taussig shunt (MBTS), performed with a prosthesis of microknitted Dacron, for the ductus-dependent tetralogy of Fallot (TOF) in early infancy. Nine MBTSs for eight patients, 4 with and 4 without pulmonary atresia, were performed, and one patient died. The mean age was 30 +/- 27 days, and the mean weight was 3460 +/- 770 g at the initial MBTS. In the initial two cases, the patients experienced convulsions due to severe hypoxia on account of the troubles of the preoperative administration of Prostaglandin E1 (PGE1). Thereafter, in order to prevent brain damage, we performed the MBTS following short-term administration of PGE1 (2-13 days). Consequently, we did not experience brain damage in later cases. Half of the patients with the MBTS with a 5 mm diameter prosthesis experienced postoperative congestive heart failure due to excessive pulmonary flow, and one of them died. The patients with the MBTS with a 4 mm diameter prosthesis had good postoperative courses. The suitable shunt flow in these patients was estimated to be 70-90 ml/kg/min. The MBTS with a 4 mm prosthesis obtained the lower level of this suitable shunt flow, but that a 5 mm prosthesis induced excessive shunt flow. Observing the patients' weight gain and the progress of polycythemia until two years of age, there were no differences between the MBTS with a 4 mm prosthesis and that with a 5 mm prosthesis. From these results, we recommend a 4 mm microknitted Dacron prosthesis for the MBTS of the TOF in early infancy.(ABSTRACT TRUNCATED AT 250 WORDS)