By combining neurochemical measurement of norepinephrine (NE) with double-label immunocytochemistry for tyrosine hydroxylase-positive (TH+) noradrenergic nerves and specific lymphoid markers, we have examined the developmental compartmentation of noradrenergic nerves in the rat spleen. TH+ nerve fibers were present in the white pulp of the spleen at birth, among surface IgM-positive (sIgM+) B lymphocytes at the outer border of the periarteriolar lymphatic sheath (PALS), distant from the central artery. During the first 7 days, noradrenergic innervation developed rapidly, forming plexuses of nerve fibers along the central artery and its branches, among T and B lymphocytes of the PALS, and along the developing marginal sinus where ED3+ macrophages accumulate. The splenic concentration of NE (per mg wet wt.) and 3-methoxy-4-hydroxy-phenetheleneglycol (MHPG), a NE metabolite, increased rapidly during this period, suggesting that NE is available and released from these nerves. From 7-14 days, the white pulp expanded to include an inner PALS, outer PALS, marginal sinus, and marginal zone; during this period, TH+ fibers arborized principally among T lymphocytes of the inner PALS and adjacent to macrophages along the marginal sinus. By 14 days of age, NE concentration reached adult levels, although the MHPG/NE ratio (an index of NE turnover) remained higher throughout development than in adulthood. Finally, from 14-28 days, the outer PALS expanded to include follicles containing sIgM+ B lymphocytes. At the earliest stages of follicular development, a parafollicular rim of noradrenergic fibers was present, providing occasional branches which arborized within the follicle. No further changes were observed in either noradrenergic innervation or cellular compartmentation after 28 days of age. These findings suggest that noradrenergic fibers are present in developing compartments of the spleen at the earliest stages of their development, providing norepinephrine for interaction with a variety of adrenoceptor-bearing lymphoid and nonlymphoid cells.