Confirmed isolates of nontoxigenic Corynebacterium diphtheriae in England and Wales increased substantially from 1986 to 1994. Ribotyping of 121 isolates confirmed in 1995 showed that 90 were of a single strain isolated exclusively from the throat; none had previously been identified in toxigenic strains from U.K. or non-U.K. residents. The upward trend in nontoxigenic C. diphtheriae probably represented increased ascertainment, although dissemination of a particular strain or clone may have been a factor.