The lectin mitogens Con A and PHA administered in vitro stimulate preferentially proliferative response of T lymphocytes. The response is accepted as a reflective for feature of immune competence of responding cells. The accessibility of specific phytomitogens for experimental determination of T lymphocyte properties creates a comfortable investigative circumstances. The authors explain why the nature of the population of B lymphocytes excludes the existence of a similar specific universal experimental tool, which could reveal complex immune properties of the population. The mechanisms of in vitro influence of putative candidates for being the B cell mitogens (PWM, LPS) are shortly presented and discussed. On the grounds of these data authors suggest that no PWM nor LPS can be estimated as a specific and selective mitogens for B lymphocytes.