The composition of a defined nongrowth medium used in stage II development of competence of Haemophilus influenzae affects the course of this development. The development of competence in two nongrowth media, M-IV and M-V, is rapid, logarithmic, and independent of the cell concentration. This last property indicates that there is probably no transfer of a competence factor from competent to noncompetent cells, in contrast to results reported for other organisms. Levels of competence reached in these completely defined media are such that 1 to 5 % of the cells are transformed in the presence of an excess of marked deoxyribonucleic acid. The method of evaluating competence, which depends on the frequency of multiple independent transformations, has been reexamined. This and other methods are compared on samples taken from a culture during development of competence.

A chemically defined medium (MI0) is described in which cells of Haemophilus influenzae Rd grow rapidly (generation time, 35 4 5 min) and reach a stationary level of 1010 cells/ml. Our strain of cells grown in this medium developed high levels of competence when transferred to another medium designed for that purpose. Conditions governing the total development of competence in this organism have now been defined.