It has been suggested that the human immunodeficiency virus (HIV), and thus the 
acquired immunodeficiency syndrome (AIDS) it causes, was inadvertently 
introduced to humans by the use of an oral polio vaccine (OPV) during a 
vaccination campaign launched by the Wistar Institute, Philadelphia, PA, USA, in 
the Belgian Congo in 1958 and 1959. The "OPV/AIDS hypothesis" suggests that the 
OPV used in this campaign was produced in chimpanzee kidney epithelial cell 
cultures rather than in monkey kidney cell cultures, as stated by H. Koprowski 
and co-workers, who produced the OPV. If chimpanzee cells were indeed used, this 
would lend support to the OPV/AIDS hypothesis, since chimpanzees harbor a simian 
immunodeficiency virus, widely accepted to be the origin of HIV-1. We analyzed 
several early OPV pools and found no evidence for the presence of chimpanzee 
DNA; by contrast, monkey DNA is present.