We investigated the benefits of adding the medicinal plants sumac and thyme at 1, 2 or 3 of the diet for male Ross broiler chicks, with four replicates of ten birds in each treatment group and a Control. ...There was evidence of higher antibody titers to Newcastle disease and influenza in supplemented chickens. It is concluded that both thyme and sumac offer potential to reduce fat content and improve disease responsiveness in broiler production systems....