An accumulation of L-dihydroxyphenylalanine (DOPA) in the median eminence of female rats treated with 3-hydroxybenzylhydrazine (NSD 1015), and inhibitor of aromatic L-amino acid decarboxylase (DOPA decarboxylase) activity, was associated with a decreased concentration of dopamine in the median eminence and pronounced reduction in the release of dopamine into hypophysial portal blood.