A radiolytic isotope is a particle which was toxic to Humans, Vulcans and Denobulans, among other species. Takrets were known to be immune to it.

In 2152, the Enterprise NX-01 encountered a massive neutronic storm which was saturated with radiolytic isotopes, forcing the crew to take refuge in a catwalk running the length of one of the warp nacelles. (ENT: "The Catwalk")