Abstract  The binding of the competence factor to cellular receptors of physiologically non-competent cells ofPneumococcus was followed as a function of time. A transformation medium without bovine serum albumin was used to study the binding of the competence factor. Control cells without the added factor remained completely non-competent under these conditions. The maximal binding of the factor to the cellular receptors took place already after 3 min of contact of the cells with the factor at 37°C. After 10 min, when the maximum induction of competence occurs in the system used, the competence factor is fully released from the receptors to the medium. It follows that within the period between the 3rd and 10th min, when the cells are being modified for the irreversible binding of DNA, the presence of the competence factor on the cells is no longer necessary.