Dear All, I am trying to translate some code in SAS about longitudinal data in R. I have found among the predefined covariance structures for repeated measures in the PROC MIXED the following: type=UN at AR(1). 'Kronecker product structure of the variance?covariance matrixi =dimni (E?V),V, where and V, respectively, are (q?q) and (p?p) positive denite matrices. The matrix represents the variance?covariance matrix between the measurements on all response variables at a given time point. It is assumed that it does not depend on a particular time point and is the same for all time points. The matrix V is the correlation matrix of the repeated measures on a given response variable, and is assumed to be the same for all response variables.' Is it possible? TIA Giovanni -- dr. Giovanni Parrinello External Lecturer Medical Statistics Unit Department of Biomedical Sciences Viale Europa, 11 - 25123 Brescia Italy Tel: +390303717528 Fax: +390303717488 email: parrinel at med.unibs.it