In Reply.—It is an honor to have one's work noted by others active in the field and comforting to see that questions thereby raised have been addressed.
In our study, endogenous peroxidase activity was blocked with hydrogen peroxide in methanol, and nonspecific endogenous antigen/antibody activity was countered with a blocking antigoat serum. Extraneous alkaline phosphatase reactions were precluded by choosing avidin-biotin complexed with horseradish peroxidase instead of alkaline phosphatase, and by incubating hybridization slides at temperatures sufficient to denature alkaline phosphatase. Most importantly, if background antigenicity were responsible, it would also have been seen in the negative controls that were concurrently run with each sample; they were universally negative.
Dr Nuovo's suggestion that polymerase chain reaction and Southern blot analysis might more specifically characterize HPV's presence is correct, and we are currently using those techniques to clarify which virotype is responsible. However, use of such techniques for screening is