While acceptance of the multirule quality control procedure is widespread in clinical chemistry, its use is minimal in the coagulation laboratory. We have applied the multirule control chart to the quality control of prothrombin time and activated partial thromboplastin time assays. Approximately 5 months were required to optimize and teach a multirule control procedure to three shifts of ST AT laboratory employees. The controlprocedure consists of the 12s control rule for screening control observations and the l3s and the 22s control rules for rejection of analytical runs. We have found that the multirule control chart is an excellent device for demonstrating the need for system maintenance and reconstitution of coagulation controls and reagents.