To evaluate instrument sterilization procedures in Minnesota, biological indicators were used to monitor 406 sterilizers in 381 dental offices. Findings suggest a general improvement in instrument performance over that of a decade ago, but sterilization failure rates are still too high. Sterilizer operator errors are a major cause of sterilization failures. BIs are useful in monitoring sterilization performance only when sterilization procedures are performed consistently and competently by well-trained staff using adequately maintained equipment.