Abstract <p>Behavioral reactions of the freshwater pond snail (<i>Lymnaea stagnalis</i> L.) have been studied under the prolonged action of 1 and 10 mM sodium and potassium nitrite solutions. It is found that 10-mM sodium nitrite solution leads to the death of one-third of the animals by the seventh day of the experiment, while 1-mM NaNO₂ and 1- and 10-mM KNO₂ solutions do not cause a statistically significant change in the number of mollusks throughout the entire experiment. The action of sodium nitrite (1 mM) is associated with a decrease in the respiratory act duration and an increase in the speed of locomotion, but does not affect the frequency and total duration of lung respiration. The effects of potassium nitrite (1 mM) are reduced to a decrease in the duration of the respiratory act and total lung respiration, but do not affect the respiratory rate and locomotion. In the control group, the above indicators do not undergo statistically significant fluctuations over the course of the experiment. It is assumed that the cationic component of the salt, primarily potassium, is capable of modifying the action of its anionic component (nitrite anion or its derivative nitric oxide), and the effects of cations (Na and K) should be considered the main ones in the prolonged action of the abovementioned compounds.</p>