The Neurospora crassa photoreactivating enzyme has been assayed for by the Hemophilus influenzae and Bacillus subtilis transformation systems. In contrast to the H. influenzae system, u.v.-treated transforming DNA from B. subtilis did not give evidence of reactivation of u.v. lesions by crude enzyme extracts from N. crassa when exposed to photoreactivating light. The u.v. dose required to inactivate B. subtilis transforming DNA is about ten times that required to inactivate H. influenzae DNA to the same level of survival. This difference in dose required to inactivate DNA's of about the same base composition probably reflects the greater u.v. resistance of the B. subtilis recipient strains used. Hypotheses are considered which suggest that N. crassa crude enzyme extracts contain either nucleases which degrade B. subtilis transforming DNA excessively or an inhibitory factor which affects the transformation process itself.