Subsurface samples from a rapid infiltration wastewater system under construction at Ft. Polk, LA were examined by employing aseptic sampling devices, acridine orange (AO)-fluorescent cell counts, and transmission electron microscopy (TEM). Samples contained 1 to 10 million AO-fluorescent bacteria per g dry wt. The Ft. Polk samples also contained forms that may have been eukaryotic microorganisms. Plate counts were very low, usually less than 100 colony forming units (CRU) per g dry wt. Since total organic carbon (TOC) was invariably less than 0.1% in the samples, attempts were made to cultivate the indigenous bacteria on low-nutrient media; but very few isolates were obtained.