In the 17 April issue, Doolittle and Sapienza and Orgel and Crick separately used the term ‘Selfish DNA’ to describe certain DNA sequences in eukaryotic organisms. They argued that the process of DNA replication allows the accumulation within the replicating genome of DNA sequences which have no functional (phenotypic) significance but whose presence stimulates the further accumulation of sequences of the same kind. This ‘selfish’ DNA is supposed, in particular, to account for some of the apparently functionless DNA in the genomes of higher organisms. The two articles have stimulated a great deal of comment, some of which appears below. The original authors will reply at a later stage.