The specifity of operation and maintenance of laboratory diagnostic systems does not allow to unconditionally use existing models of operation efficiency estimation developed for informational-measuring systems. The information theory allows to remove the inconsistency between functional and physical approaches in the efficiency estimation. The model of a priority aspect of computer laboratory systems (CLS) efficiency is constructed as a measure of correspondence of the system operation outcomes and the objectives put forvard. Numerically the CLS operation objective is expressed through the value of the information about a symptom for the process of diagnosing. The contribution of the CLS operation outcomes to the process of the diagnosing is expressed both through the internal informational characteristics of the system, and through particular characteristics of a laboratory research method efficiency realized by a given CLS.