There are several different approaches to microbiological analysis of body fluids which have been applied to sophisticated instrumented systems performing one or more parts of this analysis. Among the principles of action used in instrumented systems either on or approaching the market are radiometric assay, photometry, and electrical impedance. The operation of instruments is automatic after the culture vial containing the properly prepared sample is placed in the instrument. H. H. Johnston Laboratories manufactures various separate Bactec instruments, each suited to a particular type of investigation and/or sample load. Anaerobic culturing with the Bactec instruments requires the use of an anaerobic culture gas, usually nitrogen containing 5% H2 and 10% CO2. The basic Bactec system, comprising the Bactec instruments and clinical media, is fully developed. Market acceptance of the Bactec system is good. User experience is always the prime determinant of final acceptance in the critical and hence conservative market for clinical laboratory instrumentation.