A quantitative investigation was conducted on the antimicrobial effect of lemon extract against some food spoilage microorganisms: yeasts, Bacillus species, and lactic acid bacteria. Growth kinetics and dose-response profiles were determined from experimental data obtained with a suitable macrodilution methodology based on a turbidimetric technique. Growth and no-growth status of microbial suspensions were expressed in terms of noninhibitory concentration (NIC) and MIC. Lemon extract was effective in inhibiting the growth of the investigated vegetative cells and spores of microorganisms; effects were similar for bacteria and yeasts. The NICs for all microorganisms were very small, at around 10 ppm. Based on MICs, among the Bacillus species, the more resistant was Bacillus licheniformis. For yeasts, Saccharomyces cerevisiae was the least resistant, and similar results were obtained for Pichia subpelliculosa. Candida lusitaniae had an MIC of more than 100 ppm. Both Lactobacillus species were more resistant to lemon extract; concentrations necessary to provoke complete inhibition were approximately 150 ppm.