Peripheral blood stem cells (PBSCs) were collected for autotransplantation in 20 children (median age 4 years, range 0.5-10 years) weighing < 25 kg (median 14.5 kg, range 6.8-24 kg) with various malignant diseases: leukemias and lymphomas (n = 6), solid tumours (n = 14). Cytaphereses were carried out after standard chemotherapy (n = 10), mobilizing high-dose chemotherapy (n = 9) or radiotherapy alone (n = 1). In 13 children PBSCs were harvested after haematopoietic growth factor (HGF) administration. PBSCs were collected using a continuous flow blood separator (Cobe Spectra). In 13 patients access was through a central catheter with peripheral venous return, in 4 patients access was through a central catheter with return through a femoral catheter; one patient had femoral catheter access with peripheral venous return and two patients had both access and return through peripheral veins. For 19 patients the extracorporeal line was primed with red blood cells. The median blood flow rate was 13.8 ml/min (range 7-22 ml/min). Sixty-six procedures (mean 3.3/patient, range 1-4) were performed with a mean total collection time of 8.5 h. The median number of granulocyte-macrophage colony-forming units (CFU-GM) collected was 37.7 x 10(4)/kg (mean 107 x 10(4)/kg, range 1.05-882 x 10(4)/kg). The number of CFU-GM collected per procedure in children with HGF was 7.8-fold higher than in children without HGF (median 20.4 versus 2.6 x 10(4) CFU-GM/kg body weight, respectively). There were no consistent effects on peripheral blood counts except on platelet counts which decreased following each procedure (median decrease in platelet count was 36%).(ABSTRACT TRUNCATED AT 250 WORDS)