Three biosensor configurations that included a dissolved oxygen electrode and yeast cells (Saccharomyces cerevisiae) were evaluated as a means to assess the environmental effects of toxic chemicals. The configurations were: closed suspension—assay medium closed to air and cells suspended in the medium; open suspension—assay medium open to air and cells suspended in medium; and biofilm electrode (BFE)—assay medium open to air but cells immobilized on the surface of the electrode. The BFE was the most advantageous configuration based on assay times and detection limits.