Lergotrile mesylate is an ergot alkaloid derivative modified to eliminate the vasoconstrictive properties of the parent compound while preserving the properties that inhibit pituitary secretion. Administration of the drug to women with amenorrhea-galactorrhea resulted in the lowering of serum prolactin concentrations. The duration of action was short, so that prolactin levels were near base line 6 to 8 hours after a 2.0-mg dose and morning prolactin concentrations were not persistently suppressed. Initial therapy was accompanied by the development of postural hypotension. Tolerance to this side effect of the drug developed after several days of treatment with gradually increasing doses. In one patient, long-term treatment resulted in reduction of breast secretions, resumption of menses, and conception.