59 patients with active pulmonary tuberculosis were evaluated in terms of haematological indices, iron-related measurements and markers of inflammation. The variables evaluated included the Hb, mean cell volume (MCV), serum iron, total iron-binding capacity, percentage saturation, serum ferritin, erythrocyte sedimentation rate (ESR) and C-reactive protein. In addition, marrow iron stores were assessed both histologically and chemically. Among the changes noted was a raised S-Ferritin, which appeared in part to be a component of the acute phase response, since it correlated with C-reactive protein concentration (r 0.59, p less than 0.0001). In addition, there was a good correlation between the S-Ferritin and the concentrations of non-haem iron in the marrow, as assessed chemically on trephine biopsies (r 0.78, p less than 0.0001) and histologically on aspirated and biopsy material (rS 0.78, p less than 0.0001 and rS 0.68, p less than 0.0001, respectively). Furthermore, the quantitative relationship between the S-Ferritin and the chemical concentrations of non-haem iron in the marrow was similar to that found previously in a heterogeneous group of subjects without infections. While the present findings confirm that iron is diverted into reticuloendothelial stores in active pulmonary tuberculosis, no evidence was found to suggest that the anaemia which was present in 45 of the 59 patients was secondary to iron-deficient erythropoiesis; the percentage saturations in the 2 groups were 30.3 and 31.1 respectively. In a final analysis, the present findings were compared with previous ones obtained in a group of patients with Hodgkin's disease. The degree of rise in the S-Ferritin for a given marrow non-haem iron concentration was significantly less in the patients with tuberculosis (p less than 0.0001).