Summary Uracil was incorporated into all three bacteriophage φ6 dsRNA segments throughout the infection cycle; the rates of incorporation into each of the three segments were approx. constant for the first 15 to 20 min and then increased rapidly until 50 min after infection. The medium and small dsRNA segments were produced in greater amounts than the large dsRNA segment at all times in the infection cycle. Inhibition of host RNA and protein synthesis with rifampin and chloramphenicol revealed that virus dsRNA synthesis immediately after infection was independent of either host function.