Abstract

1. Biological and spectroscopic investigations indicate that the colour change occurring in 4:4'-diamidinostilbene, 4:4'-diamidinotolane and 4:4'diamidino-α-methylstilbene following exposure to sun and air in the solid state for periods of 8-14 months is not accompanied by significant changes either in toxicity or in absorption spectra.

2. In the case of stilbamidine slight loss of therapeutic activity was noted after 14 months only with minimal doses.

3. Stilbamidine which has become yellow from exposure undergoes the same increase in toxicity in solution as the unexposed solid.

4. The dihydrochlorides of the aromatic diamidines investigated may safely be used clinically after long exposure to air and sunlight as solids.