The use of a composite response to estimate the relative potency in a multivariate parallel–line bioassay is described by Finney (1). Occasionally a multivariate bioassay has multiple drugs also. Such a situation arises, for example, when a treatment contains several drugs. A procedure for combining multiple responses and combining multiple drugs is proposed in this paper, in order to obtain point and interval estimates of the relative potency. A composite response and a composite dose level for this purpose are obtained by using canonical analysis.