Title: Specific reliability of endurance shuttle swim test to 10 m, to 400 m free style test at population of water polo players in relation age. Objectives: The aim is to approximate specific reliability of test for assessing endurance abilities at water polo players Methods: The work is a theoretical - empirical study, with the observation as the main research method. As the cross-sectional survey, testing was used as the basic method for data collection. A total of 15 participants were included in the study. The test set was created by the SK Usti nad Labem water polo players in the age category (18-22 years). The average age was 18.47 years (SD ± 1.20). Endurance Swimming Shuttle Test at 10 m made by Rechichi (2000) was used. We used test-retest method for the stability measure. Furthermore, the determination of the content equivalent of this test to the 400 m free swimming test was used to analyze the data obtained using descriptive statistical methods. Once the assumptions for parallelism of the tests were met, we used the correlation coefficient to approximate the specific reliability in the form of content equivalence and test stability. The Bland- Altman plot was used to assess of normality. Results: The reliability test (VCP) determined by the test-retest method Rel = 0.99. This result is...