The nucleotide sequence of the 5′ end of bacteriophage Qβ RNA has been determined by a new method involving partial synthesis of the RNA in vitro. Neither of the codons commonly associated with the initiation of protein synthesis (AUG and GUG) was found before position 62. The sequence required for the initiation of synthesis of the coat protein (PuUGGCN) is not within the first 300 nucleotides from the 5′ end. A very stable hydrogen-bonded loop seems to exist close to the 5′ end of the molecule. © 1969 Nature Publishing Group.