Since arterial blood oxygen tensions are used in the evaluation of treatment of patients with meconium aspiration syndrome, it is important to recognize the occurrence of significant right-to-left shunting via a patent ductus arteriosus. The clinical findings, evidence of right-to-left ductus shunting, and outcome in eight patients with meconium aspiration syndrome are presented. Administration of tolazoline HCl and curare produced a beneficial effect on their PaO2 values.