The major part of the substantial gamma-resistance of wild-type Schizosaccharomyces pombe appears to be due to prereplicative recombinational repair mechanisms. The existence of a second "prereplicative G2" repair pathway, specific for gamma-induced damage, has now been deduced from studies of the effect of the repair inhibitor caffeine on gamma-irradiated G1 phase and G2 phase cells. only G2 cells are additionally inactivated on exposure to caffeine after gamma-irradiation. This shows that both known caffeine-sensitive gamma-repair processes (Gentner and wener, Molec. gen. Genet. 145, 1-5 [1976]) are dependent on the presence of a duplicated genome (2c) at the time of radiation exposure. Pathway I is the known "prereplicative G2" repair process (Fabre, Radiation Res. 56, 528-539 [1973]) which is involved in both UV- and gamma-repair, and which requires post-irradiation protein synthesis for activity. Pathway II represents a second distinct "prereplicative G2" repair mechanism; it differs from the first in that it is specific for repair of gamma-induced damage and appears to be constitutive.