To examine the factors contributing to microbial heterogeneity, the US Department of Energy Subsurface Science Program has initiated research at a Coastal Plain site near Oyster, VA. Sediments at the site are composed of unconsolidated, fine to coarse beach sands and gravel. The influence of microbiological culture media on the measurement of colony-forming units (CFU) and microbial diversity was examined in this study. Two low-nutrient media formulations (i.e., dilute peptone, tryptone, yeast extract, and glucose medium [PTYG] and a soil extract medium) gave equivalent estimates of CFU (maximum of about 6.5 x 10(5) CFU/g). However, a higher nutrient medium, organic nutrients with brain-heart infusion (N/BHI), gave lower numbers than the dilute PTYG. A medium used to enumerate fungi also gave significantly lower counts than the dilute PTYG medium. Although the correlations were highly significant among total CFU numbers measured with the different types of media, we found few significant correlations in several indices of microbial diversity, and the correlation coefficients were below 0.25. Thus, CFU was a relatively robust measurement,but microbial diversity was not consistent between the media. Species richness was highest with the higher nutrient N/BHI medium, and N/BHI may be a better choice for a study of diversity as determined by colony morphology.