Several enzymes with ribonuclease H specificity have been identified in bovine lymphoid tissue. Their nomenclature and some of their properties have been reported previously. In this study the time course of the induction of the different ribonuclease H activities during the stimulation of resting bovine lymph-node cells with concanavalin A was investigated. The activity of one of these enzymes (ribonuclease H IIb) increases in parallel with the induction of uridine incorporation and is well separated from the induction of ribonuclease H I, which increases together with DNA synthesis. These data indicate that the different ribonuclease H activities serve different physiological functions. They suggest that ribonuclease H I belongs to the set of enzymes which are involved in DNA synthesis.