The western end of the Insch igneous complex, northwest of Aberdeen, eastern Scotland, is a granite-diorite association not directly connected with the gabbros which make up the greater part of the complex. The granitic and syenitic varieties are fairly uniform, but the diorites are quite varied and contain xenoliths of more basic rocks. These rocks are all later than the gabbros, and it is suggested that the diorites resulted from contamination of the magma producing the granites and syenites, possibly by the gabbros. Chemical analyses are included.