A new theory of how poliovirus reaches the central nervous system (CNS) - that it enters at many peripheral nerve endings with passage along nerve pathways to the CNS, with limited dispersal in the CNS - is used in making predictions of incubation periods, and these are compared with data from the literature and with predictions from other theories. The virus transit speed along the nerve of 2.4 mm/h has been used in calculating the incubation time. The calculated incubation time for Cutter vaccinees is similar to the actual times reported, and the calculated minimal and maximal incubation times in humans are similar to the published ranges. Incubation times in different animals and for different paralyses are explained. The pathology of lesions in humans and the consequent paralyses are compatible with the model. Tonsillectomy-associated poliomyelitis is reviewed and discussed in relation to possible entry of virus from peripheral nerve endings in muscle. Increased lymphocyte concentrations in the muscle may account for continuing susceptibility after tonsillectomy. Severe paralysis following exercise is explained as an effect of increased blood supply to nerves in the CNS that has already been invaded by virus. In developing countries, the phenomenon of paralysis in the injected muscle a few hours after injection in febrile children may occur in a similar fashion. The entry of poliovirus from many sites at nerve endings in muscles is consistent with clinical, experimental, and pathologic data and provides an explanation of the incubation times and related phenomena of poliomyelitis.