The aim of the study was investigation of NO influence on fertility properties of ejaculate in the diseases of male sex organs. A total of 73 males aged 20-55 years with different sexual disorders were examined. Potentiometric assay for nitrates in ejaculate, size and shape of spermatosoa were studied. NO3 was present in all sperma samples. In the control group nitrates levels were 0.662 +/- 0.147 mmol/l. In men with sexual diseases nitrates levels in ejaculate ranged from 0.114 mmol/l to 1.530 mmol/l). In normozoospermia nitrates occurred in "mean" levels (0.295 mmol/l to 0.900 mmol/ 1). In pathospermia nitrates level was high. NO produces a protective action if it was in adequate quantity. Spermatozoid concentration and a relative number of progressive-mobile forms correlated negatively with nitrates of spermatic plasma (r = -0.40) while dead spermatozoa percentage correlated positively. Thus, low NO3 content in ejaculate may result from microcirculatory disorders and endothelial dysfunction in testicular parenchyma and epididimus. NO hyperproduction occurs in inflammatory urogenital diseases. It probably induces pathospermia via direct toxic effects of NO and stimulation of lipid peroxidation.