This paper establishes a logical framework for taking account of peak
areas when interpreting mixed DNA STR profiles. The principles apply w
herever such data are available but they are illustrated here by means
of data which have been collected from made up mixtures of known conc
entrations analyzed at short tandem repeat loci. The data have led to
some modeling assumptions which are used for numerical examples. In ac
tual casework the proportions of the various components will not be kn
own and there is a discussion of whether they should be allowed for by
integrating over a prior distribution. This is a conceptual paper, ra
ther than a prescription for casework, and the scope for further work
is outlined.