This study was designed to derive the predictive value of C-reactive protein (CRP) in peripheral venous serum of patients admitted to hospital with suspected premature rupture of the membranes (PROM). CRP was assayed by each of 4 separate methods and the results have been compared for accuracy and practical value with respect to clinical outcome and the histopathology of the placenta. Of the 4 techniques used only the latex test had characteristics suitable for a diagnostic screen. While the results were only semiquantitative, when comparisons were made to other techniques no significant change in clinical diagnosis would have been made. The results have confirmed that chorioamnionitis and preterm labour are often associated, but in some instances the extent of inflammatory infiltration was greater than might have been expected from the short time interval between documented membrane rupture and delivery. Thus it may be speculated that some cases of PROM are secondary to, rather than causative of, infection. Finally it is suggested that a controlled therapeutic trial of active intervention in those cases of PROM with elevated CRP in the absence of other clinical parameters suggestive of intrauterine infection should be undertaken.