The effect of soil:water ratio and autoclaving time on the efficiency of organic carbon extraction from soil was evaluated, and a method was developed for the routine preparation of freeze-dried soil extracts of standardized carbon contents. The optimum soil:water (w/v) ratio chosen for soil extract preparation will depend on the water-holding properties of the soil and on the subsequent use of the extract; a ratio of 1:3 to 1:5 appears optimum for preparation of freeze-dried extracts; efficiency of carbon recovery decreases drastically at ratios of less than 1:2 to 1:3. From an efficiency standpoint longer autoclaving times will yield substantial increases in organic carbon, with the most marked increase occurring within the first hour. No major differences in numbers of soil microorganisms developing on agar media prepared from diverse extracts were observed as long as the pH (6 to 7.5) and carbon content (0.1 to 2.6 g/1) of the extracts were within the normal range for soil extracts used for microbial media.