We compared the levels of latent pseudorabies virus (PRV) DNA in trigeminal ganglia (TG) of pigs after intranasal inoculation of different PRV strains by using quantitative DNA PCR. The extent of colonization attained in each case varied significantly according to the type of strain and inoculum dose, wild-type (WT) PRV being the most efficient strain in colonizing TG. When groups of pigs representing different levels of precolonization of TG with an attenuated PRV strain were challenged with WT PRV, it became evident that there is a statistically significant inverse correlation between the extent of precolonization attained by an attenuated PRV strain in TG and the level of establishment of latency by superinfecting WT PRV. The protection against WT PRV latency did not correlate with the extent of WT PRV replication at the portal of entry.