The objectives of the cross-sectional study (EpiCoS) were to describe, at different stages, volunteers offering their blood, and to characterize various ways of collecting blood. From 15 September 1996 to 31 December 1996, individuals presenting at fixed or mobile sessions in one of 11 randomly selected blood banks were included after they had a medical examination. Variables studied were relative to type of collection, individuals, medical examination, patterns of blood letting, use of collected donations and if unused, reasons for discarding. Sixty four thousand and ninety two volunteers, aged 17-66 years old were included. The proportion of exclusion during medical examination was 10.8% (95% confidence interval (CI): 10.6-11.0%). Exclusions were more frequent among new volunteers and were mostly related to the safety of recipients. Most of the 57,003 donations were whole blood (94.0%) and collected in mobile sessions (89.9%). Five percent of collected donations were discarded; 3.5% (95% CI: 3.4-3.7%) of donations discarded for biological abnormalities, including 1.5% only for initial screen reactions to infectious disease markers (HBs antigen, anti-HBc antibodies, anti-HCV antibodies, anti-HIV antibodies, anti-HTLV antibodies, malaria antibodies and anti-syphilitic antibodies). The most frequent biological abnormality was a high alanine aminotransferase level. A follow-up of these indicators, within the French haemovigilance system, should allow further identification of risk factors and high-risk contexts, and planning means of optimizing blood collection in France.