Group B Streptococcus is the most common cause of bacterial infection in the newborn. Infection in many cases causes persistent pulmonary hypertension, which impairs gas exchange in the lung. We purified the bacterial components causing pulmonary hypertension and identified them as cardiolipin and phosphatidylglycerol. Synthetic cardiolipin or phosphatidylglycerol also induced pulmonary hypertension in lambs. The recognition that bacterial phospholipids may cause pulmonary hypertension in newborns with Group B streptococcal infection opens new avenues for therapeutic intervention.