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Biosolids are nutrient-rich organic residuals that are currently used to amend soils for food production. Treatment requirements to inactivate pathogens for production of Class A biosolids are energy intensive. One less energy intensive alternative is to treat biosolids to Class B standards, but it could result in higher pathogen loads. Quantitative microbial risk assessments models have been developed on land application of Class B biosolids but contain many uncertainties because of limited data on specific pathogen densities and the use of fecal indicator organisms as accurate surrogates of pathogen loads. To address this gap, a 12-mo study of the levels and relationships between Cryptosporidium, Giardia, and human adenovirus (HAdV) with fecal coliform, somatic, and F-RNA coliphage levels in Class B biosolids from nine wastewater treatment plants throughout the United States was conducted. Results revealed that fecal coliform, somatic, and F-RNA coliphage densities were consistent throughout the year. More important, results revealed that HAdV ((x) over bar = 2.5 x 10(3) genome copies dry g(-1)) and Giardia ((x) over bar = 4.14 x 103 cysts dry g(-1)) were in all biosolids samples regardless of treatment processes, location, or season. Cryptosporidium oocysts were also detected (38% positive; range: 0-1.9 x 103 oocysts dry g(-1)), albeit sporadically. Positive correlations among three fecal indicator organisms and HAdV, but not protozoa, were also observed. Overall, this study reveals that high concentrations of enteric pathogens (e.g., Cryptosporidium, Giardia, and HAdV) are present in biosolids throughout the United States. Microbial densities found can further assist management and policymakers in establishing more accurate risk assessment models associated with land application of Class B biosolids.