In this study 13- to 14-day fetal thymic lobes were implanted within the anterior eye chambers in mice either with or without a syngeneic newborn sympathetic ganglion. It was observed after 6 weeks of implantation that the thymic lobes that grew with the ganglia had fewer lymphoid cells than their counterparts which were grown without the ganglia. The cells that developed within the thymic lobes were Thy-1- and peanut agglutinin-positive. The thymic lobes that grew with sympathetic ganglia also showed the presence of adrenergic nerves, perhaps due to reinnervation of the thymic grafts from the ganglia.