Capybaras (Hydrochoerus hydrochaeris) are the world's largest rodents and play an epidemiologic role in the transmission of zoonotic pathogens, including the causative agents of Brazilian spotted fever, leptospirosis, and others. We surveyed the health of 31 free-ranging capybaras at the Alberto Löfgren State Park, São Paulo, Brazil using a variety of diagnostic methods. Hematology and serum chemistry were consistent with mild malnutrition and parasitism but did not indicate severe physiologic imbalance or disease. All animals were serologically negative for Rickettsia rickettsii, Leishmania spp., and Trypanosoma sp., but antibodies against rabies virus (71%), Leptospira sp. (26%), and Toxoplasma sp. (23%) were detected. Salmonella sp. was not cultured from fecal samples. Frequently cultured enterobacteria included Escherichia coli (61%), Enterococcus casseiflavus (35%), Enterococcus faecalis (35%), Enterobacter aerogenes (32%), Klebisella pneumoniae (32%), and Serratia marcescens (32%). No potentially pathogenic fungi were cultured from hair samples. Fecal parasitology revealed infection by Protozoophaga sp. (58%), Viannella spp. (23%), Strongyloides spp. (10%), and Ancilostomatidae (10%). A total of 218 ticks was retrieved from the animals: Amblyomma sp. larvae and nymphs (43%), A. dubitatum adults (52%), and A. cajennense adults (5%). The capybaras were free from most potentially zoonotic pathogens evaluated; however, the presence of Amblyomma spp. ticks (potential vectors of Rickettsia spp.) and indirect evidence of exposure to the rabies virus, Leptospira sp., and Toxoplasma sp. warrant the maintenance of public health programs and wildlife health monitoring.