The aim of this study was to estimate the local progesterone and estradiol concentrations in the endometrial tissue, to compare them with their serum concentrations and to investigate possible associations between them. Observational study. The concentration of (P4) and estradiol (E2) were investigated in serum and endometrial biopsy samples from 58 women aged between 26 and 41 years during mid-luteal phase phase (7 days after LH surge).The endometrial samples were weighed and homogenized in a glass homogenizer with a Teflone pestle in a PBS buffer followed by centrifugation at 12,000 g for 10 minutes at 40C. The obtained supernatant was used for P4 and E2 measurement by electrochemiluminescence immunoassay (ECLIA) on the Cobas e411 analyser (Roche Diagnostics, Mannheim, Deutschland). Statistical analysis was performed using SPSS v.21 (IBM Corp., Armonk, NY, USA). Descriptive parameters and patient characteristics were reported as mean ± SD and median. P<0.05 was considered statistically significant. The observed endometrial P4 levels ranged from 0.001 to 270.54 ng/mg tissue, with a mean of 23.41 ± 57.63 ng/mg tissue and a median of 0.86 ng/mg tissue. The endometrial E2 concentrations ranged between 0.01 and 0.29 pg/mg tissue with a mean of 0.1±0.06 pg/mg tissue and a median of 0.08 pg/mg tissue. The determined mean P4 concentration in the endometrial tissue was 17.9 times higher than the P4 found in the serum samples, while the mean tissue E2 concentration was 1510 times lower in comparison with the E2 serum levels. As a result, the mean P4/E2 ratio (P4 [ng/mg] /E2 [ng/mg]) in the tissue (18538 ± 16638), was 136 times higher than the corresponding P4/E2 ratio in the serum (136.15 ± 85.30). A significant but relatively low Spearman correlation was found when comparing the endometrial and serum P4 concentrations (R=0.34; p=0.01). A similar relation was observed between the E2 levels in the endometrial tissue and in the serum (P=0.35; p=0.02). Again, modest but significant relation was present between the P4 and E2 tissue levels (R=0.35; p=0.02). We conclude that the mid-luteal endometrium contains relatively high levels of P4 and significantly low levels of E2 compared to their serum levels. Endometrial P4 and E2 concentrations are positively but slightly associated between each other and with their respective levels in serum.