Seven polyclonal and monoclonal antibodies were characterized for their ability to react specifically with either conformational or nonconformational epitopes of the HPV-1 virion. Using these antibodies, it was shown that the HPV-1 L1 protein (when expressed by an SV40 vector in cos cells) displayed conformational epitopes characteristic of intact viral particles. In addition, the L1 capsid protein was translocated normally into cell nuclei, was of appropriate size (57 kDa), and could be isolated in native form by immunoprecipitation techniques. Most importantly, the screening of expressed papillomavirus capsid proteins for reactivity with conformation-dependent antibodies represents a new, general methodology for ensuring that such proteins will be suitable for use in vaccine development or in the serologic detection/typing of human papillomavirus infections.