Delta sleep-inducing peptide (DSIP) supposedly involves the hypothalamus-pituitary-adrenal (HPA) axis. Previous studies have shown deviated plasma DSIP-like immunoreactivity (DSIP-LI) levels, as well as abnormal DSIP-LI responses to corticotropin-releasing hormone in patients with major depressive disorder (MDD). This study was performed to investigate plasma-DSIP-LI and its association with the dexamethasone suppression test (DST) in suicide attempters. Plasma-DSIP and serum cortisol were measured before and after dexamethasone intake in 34 suicide attempters and in healthy age- and sex-matched controls. We found significantly elevated DSIP-LI levels in MDD patients (p < .005), and a significant correlation between predexamethasone cortisol and predexamethasone DSIP-LI levels in healthy controls. Postdexamethasone DSIP-LI levels increased in subjects with low predexamethasone DSIP-LI levels, whereas they decreased in subjects with high predexamethasone DSIP-LI levels. Results give some support to the theory of glucocorticoid involvement in the regulation of DSIP, and suggest altered DSIP-LI levels in suicidal MDD patients.