It is easy to be alarmist about the release of potential mutagens into the environment on the basis of: Mutations are bad More mutations are disastrous. However, it is relatively easy to show that these equations are wrong, in that we have to take into account a number of complicating factors: Mutagen concentration ? mutational yield Segregating gene loci ? genetical damage Number of mutations ? amount of defect. The influence of these complicating factors will only appear when we have more information about the role of heterozygosity in natural populations. An adequate “perspective” on environmental mutagenesis will only be possible when the genetical structure of species, and the means of recruiting and holding genetical variation in a population have been much more thoroughly explored than hitherto.