We derive the asymptotic distribution of the sequential empirical
process of the squared residuals of an ARCH(p) sequence. Unlike the
residuals of an ARMA process, these residuals do not behave in this context
like asymptotically independent random variables, and the asymptotic
distribution involves a term depending on the parameters of the model. We show
that in certain applications, including the detection of changes in the
distribution of the unobservable innovations, our result leads to
asymptotically distribution free statistics.