Nearest neighbour analysis of nucleotides in vertebrate DNA has revealed a marked deficiency in the frequency of occurrence of the sequence CpGp. By use of the fingerprinting technique of Sanger et al. (1965) to characterise the nucleotide sequences of HeLa cell hnRNA after T1 RNAase digestion, we have shown that this deficiency also occurs in hnRNA and that it appears to be a general transcript of DNA. This is also true of the hnRNA that contains poly(A). Whilst a deficiency of CpGp occurs also in poly(A) containing mRNA from HeLa cells the deficiency is less marked than in the case of total hnRNA, or poly(A) containing hnRNA. Another difference between mRNA and hnRNA lies in the level of occurrence of the sequence UpApGp. These results are discussed with reference to the possible relationship of hnRNA to mRNA.