In the submitted paper the authors investigated the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3, calcitriol) administered by the oral route for a period of four days in amounts of 3.0 micrograms/d on prolactin secretion at rest and secretion stimulated by thyrotropin-releasing hormone (TRH) and on the lactotrophic secretory reserve assessed as the difference between values at rest and TRH-stimulated prolactin levels during the 20th, 30th, 40th and 60th minute after TRH administration (delta PRL) in 18 healthy women. The untreated control group was formed by 8 healthy women. In the subjects treated with 1,25(OH)2D3 a significant rise of the prolactin levels at rest was recorded and TRH-stimulated values and delta PRL during the 20th and 30th minute after TRH administration significantly increased as compared with control examination, while in the untreated group the values at rest and stimulated prolactin levels and delta PRL did not differ from the values recorded during the control examination. The results confirm the stimulating action of 1,25(OH)2D3 on prolactin secretion in healthy women and indicate a satisfactory reproducibility of TRH test of lactotrophic secretion.