We carried out a retrospective study on the infection rate--in episodes per 100 person months at risk (p/m/r)--of septicaemia and invasive mycoses in children with solid tumours treated at a single institution between 1985 and 1996. Among 982 patients, accounting for 8108 p/m/r, 257 infectious episodes were documented, for an infection rate of 3.2. The infection rate for "intensive" treatment was greater than that for "less intensive" treatments, 3.7 compared with 0.5, respectively; P<0.001. 58% of infectious episodes were associated with neutropenia, 22% were megatherapy-related, and 39% were related to central venous catheter (CVC), while in 13% of the episodes no risk factor was identified. Of the episodes, single organism Gram-positive bacteraemias accounted for 62%, single organism Gram-negative for 23%, multiple organism bacteraemias for 7%, invasive mycoses for 4%, and isolated fungaemias for 4%. The infection rate for Gram-positive organisms decreased significantly over time (-5.9% per year; P<0.01), but increased for the Gram-negative organisms (+3.4% per year; P=0.4). This study demonstrates that the risk of bacteraemia increases in parallel with the treatment intensity, and that a considerable number of children with solid tumours develop bacteraemia in the absence of an identifiable risk factor.