Quantitative C-reactive protein (CRP) was determined sequentially by nephelometry and photometry from a finger prick serum sample in 67 children with bacterial meningitis (BM) and 16 children with aseptic meningitis (AM). The initial mean CRP value of 180 mg/liter in children with BM differed significantly from the 12 mg/liter found in those with AM (P less than 0.001). In BM a slow descent instead of rapid normalization or a secondary increase in sequential CRP values were early indicators of complications during recovery, such as resistance to the antibiotic. A significant difference in the mean CRP values between uneventful and complicated courses of BM was observed from the fourth day on (P less than 0.001). The measurements obtained with nephelometry correlated reliably with the more widely available photometry (r = 0.99). Easily performed rapid CRP determinations can considerably improve the quality of care in meningitis patients, especially in those situations where facilities for performing bacterial cultures or antibiotic susceptibility testing are not available.