Two hundred seventy-two intubated infants who weighed less than 1751 g were enrolled in a clinical trial of phenobarbital prophylaxis of postnatal germinal matrix hemorrhage. The incidence of germinal matrix hemorrhage was 3.1% (one of 32) among infants born to women with toxemia, and 23% (55 of 240) among those born to women without toxemia. The apparent protective effect of toxemia could not be explained by intrauterine growth retardation, mode of delivery, or maternal receipt of any medication. Infants born to toxemic women were less likely than their peers to develop pneumothorax, become acidotic, and to require extensive respiratory assistance. This apparently protective effect of maternal toxemia was not seen in infants born to nontoxemic, hypertensive women. Thus, maternal toxemia, but not hypertension, might reduce the risk of germinal matrix hemorrhage by reducing the occurrence and/or severity of pulmonary and related problems that place infants at high risk of germinal matrix hemorrhage.