During 1968 and 1969, adultAlphitobius diaperinus(Panzer) were collected from turkey-brooder houses in Minnesota, Wisconsin, and South Dakota and were analyzed for bacteria and fungi. The lesser mealworms were surface disinfected, macerated, and cultured on different media; the choice depended upon experimental objectives.A wide range in the number of microorganisms was found within individual insects. Some harbored several thousand colonies, whereas others were comparatively clean.Micrococcusspp.,Streptococcusspp., and theBacillus subtilisCohn group were the most common gram-positive bacteria. Emphasis was given to gram-negative bacteria, especially those belonging to the Enterobacteriaceae group.Escherichia intermediaWerkman&Gillen was isolated from a relatively high percent of the insects.Salmonella saint paulKauffman-White occurred only in 3% of the insects, and this was from just 1 locality.Aspergillus flavusLink was the predominant fungus in the lesser mealworm, and an average of 25% was positive. Other species ofAspergillus, Penicillium,and the filamentous yeastlike fungiCandida,also were present but in relatively low numbers.