Toxicity resulting from the oxidation of methyl groups in certain therapeutic dyes seems to occur as the result of formaldehyde produced. It is suggested that ethylation be employed in lieu of the methylation to counteract this toxicity. In the triphenylmethane dyes it is found that apparent differences in staining and bactericidal value may possibly be accounted for by differences in structure, a rosaniline base in general being superior to the pararosaniline compounds.