In September, 1959, a new tetracycline compound, demethylchlortetracycline* (here-after referred to as DMCT), became available for general use. This compound is reported to be identical in structure to chlortetracycline except for the absence of a methyl group in the 6-position.1 In early studies it was found to be more resistant to acid and alkali degradation than the other tetracyclines in common use,1 and to be generally more active against bacterial pathogens than tetracycline (hereafter referred to as TC) or oxytetracycline.2-5 The amount of DMCT absorbed from the gastrointestinal tract of man following a single dose was less than with TC,6,11 but Kunin and Finland found that the serum half-life was 44% greater for DMCT than for TC, and the renal clearance of the former drug was only 43% of the latter.7 Assays of serum antibacterial activity after equal doses of the 2 drugs showed significantly