A Giemsa type formula consisting of azure A eosinate, azure B eosinate, methylene blue eosinate, and methylene blue (88%) in proportions approx. 1, 5, 4, 1, respectively, shows advantages over similar formulae consisting of pure thiazin dyes in constancy of composition, and consequent ease of prepn. The method for preparing the necessary eosinates is described. The formula recommended stains malaria parasites in both thin and thick blood-film preparations, and other blood parasites.