OBJECTIVE To determine the ability of a commercially available biological indicator (BI), used to monitor steam and ethylene oxide sterilization, to biologically monitor a liquid sterilization process consisting of a sterile processor, a proprietary peracetic acid sterilant, and a sterile rinse system. METHODS Analysis of spore survival in BIs tested in STERIS SYSTEM 1 liquid chemical sterilization processor and in vitro. METHODS STERIS Corp. research laboratory. METHODS In vitro tests were performed in the STERIS SYSTEM 1 Processor using 12-minute and 6-minute sterilant exposure cycles. D values (time to inactivate one log of spores), spore washoff and outgrowth time, and inhibitory effects of the sterilant were determined. RESULTS Sterilization of the spore-inoculated filter paper strips in the BIs was ascertained in both processor testing and in vitro tests using conditions identical to those in the processor. The extensive washing and dilution during the processor cycle resulted in only 0.2% and 1.8% removal of the spores from Bacillus stearothermophilus and Bacillus subtilis inoculated spore strips, respectively. Carryover of the diluted sterilant to the culture medium did not inhibit the outgrowth of the spores, and D values could be obtained. B stearothermophilus was two to three times more resistant to the sterilant than B subtilis. However, either spore meets the performance specifications applicable to BIs for monitoring sterilization processes. CONCLUSIONS The data demonstrate that the commercial BIs evaluated are reproducible and verifiable indicators of the liquid chemical sterilization process. The same kind of performance specifications for producing BIs used to monitor steam or ethylene oxide systems also apply to the evaluated liquid chemical sterilization system.