Abstract 1. 1. Disc electrophoresis was used to study the oscillations during a 24-hr period in the concentration of proteins in the hemolymph of male Madeira cockroaches, Leucophaea maderae (F.), conditioned to 12 hr light-12 hr darkness for 26 days. 2. 2. Maxima in the concentrations were observed after “dawn”, close to “sunset” and during the latter portion of the dark period.