INTRODUCTION: Prolactin is a polypeptide hormone secreted by adenohipophysis. Different molecular forms of prolactin in the circulation affect its biological activity. Increased concentration of monomeric prolactin in the blood causes true hyperprolactinemia, whereas macroprolactin is the most common cause of asymptomatic hyperprolactinaemia. OBJECTIVE: The aim of this study was to determine the proportion of requests for PEG precipitation of macroprolactin in the total number of elevated prolactin concentrations and to determine the proportion of results in which the PEG precipitation method indicated the presence of macroprolactin. METHODS: In this study, the results obtained from the laboratory information system in the Clinical Laboratory of University Hospital Center Split were used. In one year period (28 June 2016 – 28 June 2017) 1300 patients who had results for the measured prolactin were singled out. Concentrations of prolactin were measured using ECLIA method on immunoanalyzer Cobas Roche e 601 and PEG precipitation method. RESULTS: From the total of 1300 samples singled out from the laboratory information system, 458 samples showed an elevated concentration of prolactin. Out of the 458 samples with elevated prolactin concentrations, for 50 of them the precipitation of macroprolactin was required. By processing and interpretation of results it was determined that 58% of the results had elevated prolactin concentrations, 16% results indicating monomeric prolactin and macroprolactin predominance, and 26% results indicating macroprolactin predominance in circulation. CONCLUSION: In the total number of results with elevated prolactin concentrations, a small proportion (11%) for precipitation of macroprolactin was required. After PEG precipitation of macroprolactin, the highest percentage of results indicated true hyperprolactinemia.