An LC–MS/MS method was developed and validated to analyze simultaneously estrogens (estradiol, E2; estrone, E1), androgens (testosterone, T; androstenedione, A4; dehydroepiandrosterone, DHEA), progestagens (17a-hydroxypregnenolone, 17OHP5; 17a-hydroxyprogesterone, 17OHP4; progesterone, P4), glucocorticoids (cortisol, F; cortisone E; corticosterone, B; 11-deoxycortisol, S; 21-hydroxyprogesterone, 21OHP4), and mineralocorticoids (aldosterone, A) from 150 μl of human serum, plasma, or endometrium and endometriotic tissue homogenates. Samples spiked with isotope-labeled steroids as internal standards were extracted with toluene prior to LC–MS/MS analysis. The chromatographic separation of underivatized steroids was achieved on a biphenyl column with 0.2 mM NH4F as the eluent additive and a water-methanol gradient to improve E2 and E1 ionization. Method validation was performed with human plasma samples, and analysis of certified E2, T, F, and P4 reference serums (BCR-576, ERM-DA346, ERM-DA192, ERM-DA347), as well as homogenates of endometrium and endometriotic tissue. A total of 27 steroids were included in the method development to ensure the specificity of the method. After validation, the method was found suitable for quantitative analysis of 11 steroids: E2 (6.7 pM-13 nM), E1 (1.3 pM-6.6 nM), T (3.3 pM-13 nM), A4 (13 pM-33 nM), 17OHP5 (32 pM-65 nM), 17OHP4 (33 pM-13 nM), F (33 pM-133 nM), E (13 pM-130 nM), B (33 pM-134 nM), S (13 pM-129 nM), and A (32 pM-32 nM). In addition, DHEA (333 pM-32 nM), P4 (13 pM-13 nM) and 21OHP4 (13 pM-13 nM) can be analyzed semiquantitatively.