Lipocortin-l, a 35 kDa member of the annexin farnily of proteins, originally evoked interest as one of the second messengers for the anti-inflammatory actions of glucocorti- coids. However, the original inference that lipocortin-1 was a glucocorticoid-responsive gene, and the implication that it mediated the anti-inflammatory action of glucocorticoids, have remained controversial and unproven, This study was performed to evaluate the effects of hydrocortisone on the expression of lipocortin-1 in cultured rat mesangial cells. We analyzed the induction of lipocortin-1 by Western blotting, and immunofluorescent staining in cultured rat mesangial cells treated with 0, 1 and 10m M of hydrocortisone for 3 days. Flow cytometry was also performed for evaluation of membrane-bound lipo- cortin-1. Hydrocortisone increased expression of lipocortin-1 in a dose dependent manner as determined by Western blot. Lipocortin-1 was induced up to 195%(cytosolic fraction) and 225%(mernbrane fraction) of control in the presence of 10 p M of hydrocortisone. Induction of lipocortin-1 was also observed by immuno Quorescent staining. Hydrocortisone increased expresssion of mnernbrane-bound lipocortin-1 in a dose dependent manner as determined by flow cytometry. Mean fluorescent intensity was increased to 276% of con- trol in the presence of 10 p M of hydrocortisone. Proportion of fluorescent-positive ceRs also increased from 3.296 to 9.3%. These results suggest that glucocorticoids induce lipocortin-1 in cultured rat mesangial cells.