It has been reported that instructed delay period (IDP) activity in PMd often covaried with the direction of intended arm movements when monkeys used either the arm contra- or ipsilateral to the recording site (Crammond & Kalaska, SFN Abst 17:308, 1991). Furthermore, the discharge directionality was often similar for both arms (i.e. not mirror-transposed). Of 60 PMd cells tested in that study, 47 showed differences in the preferred direction (PD) of IDP activity of < 45° between the two arms (mean absolute difference: 38°). Here we report similar results from a different IDP task (Cisek & Kalaska, SFN Abst 25:381, 1999). Of 22 PMd cells tested with each arm separately, 19 were directionally-tuned for movements made with either arm. The PDs of IDP activity recorded with each arm were also very similar, with 18/19 cells showing differences in PD of < 30° (mean absolute difference: 8°). The PDs for each arm were significantly different for only 2/19 cells, based on bootstrap estimates of confidence intervals....