We have previously found a dramatic increase of corticotropin-releasing factor receptor (CRF-R1) production in splenic neutrophils of male C57BL/6N mice after application of an immunological stimulus. We demonstrate here that immobilization, a predominantly psychological stress, exhibited a similar effect. Shortly after 90 min of immobilization, the number of splenic CRF-RI+ cells was transiently increased by nearly 8-fold, while it was reduced in thymus and unchanged in lymph nodes. The CRF-R1+ cells were detected by an affinity-purified polyclonal antibody directed against the N-terminus of CRF-R1, and identified as neutrophils, eosinophils or their immature precursors on the basis of their nuclear shapes, Wright-Giemsa staining and colocalization of CRF-R1 with the ER-MP58 antigen.