In this paper, the D- and D-s-optimal design problems in linear regression models with a one-dimensional control variable and a k-dimensional response variable are considered. The response variables are correlated with a known covariance matrix. Some of the D- and D-s-optimal designs with polynomial models for k=2 are found explicitly. It is noted that the number of support points for the D- and D-s-optimal designs highly depend on the correlation between the two response variables except on some special cases. (C) 2001 Elsevier Science B.V. All rights reserved. MSG: 62K05.