Infectious complications after autologous peripheral blood progenitor cell transplantation (PBPCT) have been reported in a few studies including small patient numbers. The present study was performed to assess the incidence, types, outcome and factors affecting early and late infections in 150 patients aged 18 to 68 years (median 46.5) who underwent high-dose therapy, with G-CSF. Patients were kept in reverse isolation rooms and received antimicrobial chemoprophylaxis with oral quinolone and fluconazole. One hundred and fifteen patients (76.7%) developed fever (median 3 days, range 1-29); 20 patients (55.5%) had Gram-positive and 13 (36. 2%) Gram-negative bacterial infections. There were no fungal infections or infection-related deaths. Mucositis grade II-IV (P = 0. 0001; odds ratio 3.4) and >5 days on ANC <100/microl (P = 0.0001; odds ratio 2.3) correlated with development of infection. Only days with ANC <100/microl affected infection outcome (P = 0.0024) whereas the antibiotic regimen did not. After day +30 there were four cases of bacterial pneumonitis (2.7%), one case of fatal CMV pneumonia (0. 8%) and 20 of localized VZV infection (13.3%). Reduction of neutropenia duration with PBPCT and G-CSF is not enough to prevent early infectious complications since only a few days of severe neutropenia and mucositis are related to development of early infections. However, no infection-related deaths were seen. Although Gram-positive organisms were the major cause of bacteremia, a glycopeptide in the empirical antibiotic regimen did not affect infection outcome. In PBPCT recipients, early and late opportunistic infections were notably absent, which was at variance with what was seen with bone marrow recipients. Efforts should be made to prevent mucositis and neutropenia and identify new strategies of antibacterial prophylaxis.