Naturally occurring Cronartium ribicola infections were discovered in August and September, 2004 on Pedicularis racemosa and Castilleja miniata in a mixed stand of white pine blister rust-infected whitebark pine (Pinus albicaulis) and western white pine (P. monticola) in northern Idaho, at Roman Nose Lakes, ca 30 km west of Bonners Ferry. Infections were confirmed by ITS rDNA sequencing of teliospores. The ability of these species to act as host was confirmed by laboratory inoculations using aeciospores from whitebark pine. Isolates recovered from P. racemosa after artificial inoculations were able to infect Ribes nigrum and were thus not specific to an alternate host genus, and also infected western white pine seedlings. Cronartium ribicola was detected on additional P. racemosa and C. miniata at the site in 2005. Infections were confirmed by ITS sequencing and transfer to R. nigrum. In 2005, exposure of local plants to local inoculum at a second site, ca 200 km to the south, caused infections on P. racemosa, and laboratory inoculations implicated C. rhexifolia from this site as a third non-Ribes alternate host. Identification of these alternate hosts may significantly alter our concepts of blister-rust hazard and epidemiology, particularly for those upper montane to subalpine stands where the newly identified hosts are abundant. The use of these hosts by the introduced pathogen also raises the possibility that fungal adaptation may be one factor allowing change in this dynamic and evolving pathosystem.