The nucleotide (nt) sequence at the ends of the genomes of the Streptococcus pneumoniae phages Cp-5 and Cp-7 has been determined and compared with the corresponding sequence of phage Cp-1. The genomes of phages Cp-5 and Cp-7 have inverted terminal repeats (ITRs) 343 and 347 bp long, respectively. In Cp-1 DNA the ITR is 236 bp long and the following 116 bp are 93% homologous. Some regions within the ITRs are conserved in the three genomes although the complete sequence of the ITRs is no more conserved than the rest of their genomes. The chromatographic behavior of their tryptic peptides suggests that the terminal proteins (TPs) of at least two of the phages are similar and that the TPs of the three pneumococcal phages differ markedly from that of the Bacillus subtilis phage psi 29.