Jensen (1933) claimed that the Dlm/ (DRM) m ratio of diphtheria toxin is constant, the value being 3, 000. No detailed reports on the relationship between Dim and DRM can be found.
Our previous finding; i. e., the Dlm/DRM ratio of fresh diphtheria toxin preparations is highly variable in a range from about 3, 000 to 100, 000 or higher (Kondo et .al. 1960), did not support Jensen's claim. Furthermore, the following two facts were found: 1) When crude or fractionated diphtheria toxin was partially detoxified by mild heating, by dilution with buffered saline or by f ormalinization, DRM increased faster than Dlm, and the Dlm/DRM ratio became smaller during the detoxificating process, approaching to 3, 000, the value given to the Dlm/DRM ratio by Jensen; 2) When fractionated with ammonium sulphate, fractions whose DRM/Lf ratios were different from that of the parent toxin but Dlm/Lf ratios remained constant. A tendency was also observed that the fractions precipitable at a lower concentration of ammonium sulphate had smaller Dlm/DRM ratios (Kondo et al., 1960) .
The present paper deals with some additional findings which together with the previous findings are expected to contribute a great deal to studies on the biological activity of diphtheria toxin.