Nuclear volume of neurons in the medial hyperstriatum ventrale (MHV), apart of three day-old chick brain that is concerned with learning and memory, was obtained by new stereological methods. Mean nuclear volume and coefficient of variation of the number distribution of nucleus volume was estimated by selector and point-sampled intercepts methods. In the MHV of forebrain of chick, of the same sex there is no difference between the nuclear volume of neurons in the left and right brain hemispheres. However the mean nuclear volume is significantly different between male (VV= 1670, 32±0.04 SEM 1mm3) and female chicks (VV= 1114,9±0.04 SEM mm3) with the present knowledge we could not interpret why the mean nuclear volume in the right and left MHV region of male chick forebrain is significantly bigger than females.