The COBE Spectra was evaluated in 71 plateletpheresis procedures. Using the collection and anticoagulant algorithms of the system (n = 57) we collected 4.3 +/- 1.2 x 10(11) platelets with a mean separation efficiency of 70.2 +/- 12.1%. The cell contamination was very low (leukocytes 0.5 +/- 1.0 x 10(7), red cells 1.5 +/- 2.2 x 10(7]. In four different modifications of the standard separation protocols, we tried to reduce the ACD consumption in order to shorten the donation time and to improve donor safety. A constant ACD/blood ratio of 1:9 and increase of the blood flow to 50 ml/min (n = 14) caused significantly lower yields (3.1 +/- 0.7, p less than 0.01) and visible spontaneous platelet aggregates in the collection line in 50% and in the PC's in 29% of the runs. In order to prevent platelet activation the ACD algorithm had to be maintained, but a reduction of the ACD/blood ratio to about 15% was acceptable.