Purpose — to identify the standard chemical composition of anterior chamber aqueous humour (AH) using energy dispersive spectrometer (EDS) integrated in scanning electron microscope (SEM); to study the influence of concentration gradient of chemical elements between aqueous humor and blood serum (BS) on the secretion of intraocular fluid (IOF) at normal and increased intraocular pressure (IOP). Material and methods. The study involved two groups of patients consisting of 33 people (33 eyes) each. The 1st group included patients with cataract and normal IOP (control), the 2nd group included patients with POAG and decompensated IOP. The samples (AH and BS) were taken during surgeries and studied using Oxford X-Max50 EDS integrated in EVO LS10 SEM. Results. The concentration ratios (mmol/l) of AH/BS for Na at normal IOP was 1.472/1.278, for K — 0.106/0.035. In cases with POAG with decompensated IOP, the concentration ratio of Na was 1.424/1.248, K — 0.114/0.036. The concentration ratio of N between AH in cases with decompensated IOP and AH of normotonic eyes was 1.151/0.960, for S — 0.020/0.012. Conclusion. Consistent excess of Na and K concentrations in AH compared to BS indicates active participation of these osmotically active elements in the normal process of intraocular fluid secretion. The absence of significant differences in the ratios of Na and K in AH and BS at normal and decompensated IOP indicates low significance of these elements for pathological hypersecretion of intraocular fluid. Increased concentration of N in AH eyes with decompensated IOP compared with AH at normal IOP indicates possible involvement of nitrogen-containing osmotically active substances in the abnormal hypersecretion of intraocular fluid.