Four washer-disinfectors (AdaptaScope, ETD-2Plus, Innova-E3, LS-2000) were compared. The cleaning and process efficacies of the washer-disinfectors were determined by visible examination and by microbial reduction factor (RF) using the German test method (EN ISO/TS 15883-5). Test pieces were contaminated with blood and Enterococcus faecium. Three cleaners (Cidezyme GI, ETD Cleaner, Liquid 52) and three disinfectants (Cidex OPA-C, ETD Disinfectant, Liquid 44) were used. The cleaning efficacy was also tested with water alone. Effectiveness of Cidezyme GI in the AdaptaScope was determined with an RF of 7.0, in the LS-2000 with an RF of 8.4; Liquid 52 obtained in the LS-2000 an RF of 7.0. The cleaning efficacies with water for the AdaptaScope (RF 2.1) and the LS-2000 (RF 1.2) were significantly different. Microbiological effectiveness of overall processes obtained in the AdaptaScope with Cidezyme GI/Cidex OPA-C (RF 8.4) and in the LS-2000 with Liquid 52/Liquid 44 (RF 9.2) were also significantly different. The test pieces remained contaminated at the end of overall processes in the Innova-E3 and an RF could not be established. In the ETD-2Plus the RFs after the total processes were low (3.7-7.5 and 1.8). The AdaptaScope and LS-2000 consistently produced a microbial reduction, although differences in the efficacy of the overall processes were observed. Processing endoscopes with artificially blocked channels in the AdaptaScope and LS-2000 incurred error messages and the processes stopped whereas the ETD-2Plus and Innova-E3 did not display error messages.