Data from a previous study of PPHN were analyzed. The objectives were to: identify the effects of a variety of potentially adverse prenatal exposures from interview data; formulate multi-variate models of risk of PPHN to determine if smoking or use of prostaglandin inhibitors increased the risk of PPHN; explore associations of PPHN with history of illicit drug use and maternal hypoxia; examine the relationships of postnatal care and perinatal risk factors on the incidence and outcome of PPHN; test the relationships of PPHN to the biochemical presence of nicotine and drugs in neonatal urine.