A comparative study of behavioral reactions (licking of back paw, sleeping, eating, running, washing) in mice with a genetic knockout (lines C57BL/6L and CBA/CaLac) and in control animals was carried out. Experiments have been performed in control conditions (without any influences), after a subcutaneous injection of 5% formalin solution, and also in a case when animals before an injection of formalin received analgin. It was established that the behavior of mice with a genetic knockout without any influences statistically authentically differs from mice without genotype infringements. Sleep duration in mice with a genetic knockout was 3-4 times less, and duration of eating was 5-13 times less than in control animals, but grooming (washing) was more intensive (in 2.4 times). Duration of painful reaction (licking of back paw) in response to formalin injection in mice with a genetic knockout was in 1.3 - 2.4 times less, than in mice of control group. Analgin in a doze of 8.3 mg/kg in genetic knockout mice suppressed pain more poorly, than in mice of control group. Analgesia incontrol group amounted 74.10%, and in genetic knockout mice it was 27.6-28.9%. The results allow concluding that mice with a genetic knockout differ from control animals both by initial behavior, and by reaction to a tonic pain. Analgin causes a weaker analgesic action in mice with a genetic knockout in comparison with animals of control group.