Abstract
In both sexes erythrocyte sedimentation rate (ESR) and erythrocyte volume (EV) fluctuated with age. The relationship between ESR and EV remained constant for both cocks and non‐laying hens over the whole age‐range. With the onset of sexual maturity in hens the ESR was found to be raised above the levels for non‐laying hens and another relationship between ESR and EV was established. The increased ESR at sexual maturity was related to the increase of lipophospho‐protein in the blood plasma.