In order to assay the human plasma concentration of nifedipine in patients with bronchopulmonary dysplasia (BPD) and pulmonary hypertension, a modified high performance liquid chromatography (HPLC) method was applied. The retention times for nifedipine and an internal standard (11-ketoprogesterone) were $10.5;{pm};0.41$ and $13.1;{pm};0.63$ min, respectively. Absolute recovery from the plasma was $102.9;{pm};7.07%$. Reproducibility was excellent and variability between the runs was small. There was a negligible degradation during the assay procedure. The calibration curve shows a good linearity in the range of the desired plasma concentrations of nifedipine. A stability test of nifedipine in the human plasma shows 8 and 13% degradation during the storage of 5 and 9 months, respectively. There were no interferences on the HPLC assay with any possible medications for the BPD. The method has been used to monitor the drug concentrations in a patient. The concentration-time curve of a patient after a single oral dose of 0.3 mg/kg shows a double-peak phenomenon that was quite different from the previous report, suggesting non-bolus administration. However the hemodynamic responses were corresponding to the plasma concentration levels of nifedipine.