When Y-1 mouse adrenal tumor cells were treated with sodium orthovanadate, an intermediate filament (IF) inhibitor in BHK21-F cells, there was no change in the amount of 20α-dihydroprogesterone produced. A neurofilament inhibitor, β, β'-iminodipropionitrile (IDPN), enhanced the ability of Y-1 cells to produce steroid in response to ACTH by acting on the plasma membrane. Electron microscopy of Y-1 cells extracted with Triton X-100 revealed that both vanadate and IDPN caused the aggregation of cytoskeletal and granular structures in the perinuclear area. The steroidogenic effects of IDPN suggest that the perinuclear aggrergation of cytoskeletal structures may result from the detachment of IF from the plasma membrane, while the reason for the cytoskeletal changes by vanadate is unknown.