Histidine-rich glycoprotein (HRGP) is a potent inhibitor of T cell activation and production of cytokines such as (gamma-IFN). gamma-IFN released by activated T cells is increased during a short-term period at the onset of GvHD after allogeneic bone marrow transplantation. Therefore we investigated HRGP plasma levels in patients after BMT. Blood was collected from 20 children before and up to 6 weeks after BMT. In patients without GvHD, HRGP plasma levels decreased during the first week after BMT to 237 +/- 60 micrograms/ml, compared with 302 +/- 104 micrograms/ml before transplantation. However, no significant changes in mean HRGP plasma levels were observed during the following 5 weeks of the posttransplantation period. Acute GvHD occurred in 10 of 20 patients between the second and third week after BMT. HRGP levels (mean +/- SEM) in patients with GvHD dropped during the first week to 158 +/- 32 micrograms/ml, compared with pretransplant levels of 240 +/- 48 micrograms/ml). In contrast to results in patients without GvHD, a second and significant decrease was obtained between the second and third week after BMT in patients with GvHD (161 +/- 35 micrograms/ml vs 84 +/- 13 micrograms/ml; p < 0.01). In the third week after BMT, HRGP levels were significantly lower in patients with GvHD as compared with patients without GvHD (166 +/- 29 micrograms/ml; p < 0.01). The decrease in HRGP in the second and third posttransplantation week was not a result of steroid treatment.(ABSTRACT TRUNCATED AT 250 WORDS)