Applicability of Hoffman's average of normals (AON) method was evaluated in quality control (QC) for twenty clinical chemistry assays (ALT, Alb, ALP, AMY, AST, T. Bil, inP, Glu, Ca, Cl, T. Chol, Great, CK, K, LD, T. Prot., Na, TG, BUN, Uric. A.) performed routinely in the Hospital of Medical Faculty of 9 Eylul University. Consecutive Texas Instruments XL-Dacos patient data were accumulated over 10 days. According to the guidelines developed by Cembrowsky et, al. for the implementation of average of patients (AOP) (also known as AON) procedure, the patient population mean, (X) over bar(p), population standard deviation, S-p, the ratio of S-p/S-a (S-a. the analytical standard deviation), and the approximate number of patient results averaged. Np (with P-ed=0.50) were determined from the nomogram constructed by Cembrowsky et. al., illustrating the relationship between Np, S-p/S-a, and the probability of detecting a 2S(a) shift (P-ed) when the probability of false rejection, P-fr, is 0.01. The control limits and the truncation limits were selected as (X) over bar(p)+/-2Sp and (X) over bar(p) +/- 2.58 x Spl/Np, respectively. The estimated values were assessed for the applicability of AOP procedures in the clinical laboratory. We conclude that the AOP procedure is a valuable tool for instrument monitoring as an adjunct to more costly standard QC procedures and is also an efficient, cost-effective and rapid way of collecting appropriate information on large number of patients.