We determined serum levels of the carboxy-terminal-cross-linked telopeptide and carboxy-terminal propeptide of type I collagen (ICTP and PICP) in 24 patients with acute complicated Plasmodium falciparum malaria prior to and 7, 14, 21, and 28 days after therapy by radioimmunoassay in Bangkok, Thailand. Elevated levels of ICTP were observed in patients (mean +/- SD concentration 16.7 +/- 5.8 ng/ml), compared with normal controls (3.1 +/- 1.3 ng/ml), during the acute phase of the disease. In contrast, serum concentrations PICP were not different between patients and controls (168 +/- 63 and 144 +/- 57 ng/ml, respectively). After therapy serum ICTP concentrations decreased but remained elevated even 28 days after the malaria attack (10.3 +/- 2.9 ng/ml). These findings suggest an increased production or release of ICTP in P. falciparum malaria, which could implicate an alteration of extracellular matrix during P. falciparum malaria.