Intraperitoneal injection of a single high dose of cortisol acetate into young adult BALB/c mice resulted in severe prolonged involution of the axillary lymph nodes, which started to regenerate only three weeks later. Histological and histomorphometrical analysis revealed that cortisol-induced lymphocyte depletion and diminution of lymph nodes was more pronounced in its B cell areas than in the paracortical T cell areas. Lymphocyte-depleted areas in the outer cortex i.e. in the B cell compartment, were characterized by a persisting diffuse reticular framework. Lymphocyte depletion in the paracortex resulted in partial transformation of its normal diffuse structure into "paracortical cords" with intervening patent sinuses. It was concluded that 1) T cell areas in mouse lymph nodes are more resistant to exogenous cortisol than B cell areas, and 2) paracortical cords may be interpreted as basic tissue units of the paracortical area in the mouse lymph node.