Successful cleaning of medical devices, such as flexible endocopes, has been recognized to be of major importance for effective processing. Washer-disinfectors (WD) are considered to be an important step in this direction. The cleaning process in WD, however, has only been partially assessed regarding its effectiveness, and therefore to study this in more detail, tests were carried out, according prEN ISO 15883, using transparent teflon tubes as test pieces (length 2 m). For each experiment three test pieces were contaminated with the 'German test soil' containing Enterococcus faecium in blood, two for the test and one as a control (no automatic cleaning). Automatic cleaning was performed with a Wassenburg WD 440. Ten cleaning agents were used. In addition the process was carried out with water alone. After automated cleaning, test pieces were assessed visually (four categories, range: very poor to excellent visible cleanliness) and microbiologically [log(10) reduction factor (RF)]. Each experiment was repeated three times. Using the WD water gave excellent visible cleanliness with a mean RF of 1.1+/-0.6. The same excellent visible cleanliness was obtained with seven cleaning processes: deconex 23 Neutrazym, Helimatic Cleaner enzymatic, Korsolex-Endo-Cleaner, Labomat E, neodisher mediclean, Thermosept ER, and Thermoton NR. Worse visible cleanliness was found with three cleaning processes: Olympus ETD Cleaner and neodisher FE led to adequate visible cleanliness, and the cleaning process with neodisher medizym led to poor visible cleanliness. Six cleaning processes reduced the test organism by RF>or=3, i.e. the reduction was significantly higher than after cleaning with water alone. No significant difference between use of water alone and the cleaning process was found with three cleaning processes: Olympus ETD Cleaner, neodisher mediclean, and Thermosept ER (range RF: 0.8-1.8; P > 0.05). The cleaning process with neodisher medizym yielded a significantly lower mean RF (P = 0.039) in comparison with water treatment alone. Both visible cleanliness and mean RF, varied indicating that the choice of cleaning process had a major impact on the overall result.