Cost comparison of two comparably effective techniques of plateletpheresis, a manual method and an automated discontinuous flow centrifugation technique, is presented using a hypothetical model. The former procedure costs $62.48 per pheresis for disposables and labour as opposed to $78.32 per pheresis for disposables and labour for the latter. The annual volume of plateletpheresis at which the accumulated costs equal the total charges, i.e. the 'break-even' point, is calculated and found to be 63.7 for the automated technique and 10.9 for the manual method, if the charge for each is $200.00. For the manual method at a current charge of $80.00, the break even point is 85.8. The assumptions underlying this hypothetical model are examined, and the effects of deviation from these assumptions are analyzed in terms of the break even point. Cost accounting of plateletpheresis is shown to be dependent upon the choice of approach to allocation of costs, the assumptions of the cost accounting model, and the selection of an appropriate charge.