Among a number of carbohydrates studied, glucose, fructose, and sucrose were found to support adequate growth in five Staphylococcus aureus strains selected for their different properties: toxinogenic Wood 46, auxotrophic Wood 46 thy−, encapsulated Smith, penicillin-resistant Saskatchewan 755, and non-toxinogenic and coagulase-negative SA-13.In all these strains, the analog 2-deoxy-D-glucose (deGlc), when included in the culture medium inhibited growth by blocking the use of sucrose or fructose almost completely; D-glucose restored normal growth. A Wood 46 thy− strain was more specifically used to study the effects of deGlc on "balanced and unbalanced" growth and formation of toxin. When added at the beginning of the logarithmic phase of growth in the presence of thymine, deGlc lowered the growth rate of the cells; on the other hand, as expected, penicillin (affecting formation of cell wall and used here for comparison purposes) had a truly killing effect. Thymineless death associated with "unbalanced" growth was inhibited by deGlc and this inhibition was not significantly reversed by glucose. The cells were observed under the fluorescence microscope, after staining with conjugates of rhodamine and lysozyme, as well as with those of fluorescein and anti-Staphylococcus aureus rabbit serum. When grown in the presence of deGlc, the cells were seen as unevenly stained fluorescent dots, while some of those treated with penicillin or undergoing thymineless death appeared as large and amorphous fluorescent bodies, unlike the untreated cells; such changes due to deGlc or penicillin could possibly involve carbohydrate-containing antigens (e.g., mucopeptide and teichoic acid). The results obtained with the use of various standard techniques to detect toxin indicated that toxin formation is inhibited by deGlc, apparently not selectively but proportionately with growth.