In Alcaligenes eutrophus CH34, determinants encoding inducible resistance to chromate (chr) and to cobalt and nickel (cnr) are located adjacent to each other on plasmid pMOL28. To develop metal-sensing bacterial strains, a cloned part of plasmid pMOL28, which contains both determinants, was mutated with Tn5-lacZ. The chr::lacZfusions were specifically induced by chromium; cnr was induced best by Ni2+ but was also induced by Co2+, Mn2+, chromate, Cu2+, Cd2+, and Zn2+. The broad-host-range IncP1 plasmid pEBZ141, which contains achr::lux fusion, was constructed.A. eutrophus AE104(pEBZ141), carrying achr::lux transcriptional fusion, could be used as a biosensor for chromate when cultivated in glycerol as an optimal carbon source. Chromate and bichromate were the best inducers; induction by Cr3+ was 10 times lower, and other ions induced only a little or not at all. Interactions among induction of the chr resistance determinant, chromate reduction, chromate accumulation, and the sulfate concentration of the growth medium were demonstrated.