The use of hydroxyphenyl-1,3-propanediones of formula: ##STR1## wherein R.sub.1 and R.sub.2 are each independently of the other hydrogen, C.sub.1 -C.sub.12 alkyl, C.sub.1 -C.sub.12 alkoxy, trifluoro-C.sub.1 -C.sub.3 alkyl, phenyl or halogen; R.sub.3 is a 5- or 6-membered heteroaromatic radical; thiophenyl; or a radical of formula: ##STR2## R.sub.4, R.sub.5, R.sub.6 and R.sub.7 are each independently of the other hydrogen, halogen, C.sub.1 -C.sub.12 alkyl, C.sub.1 -C.sub.12 alkoxy, carboxy or trifluoro-C.sub.1 -C.sub.3 alkyl; in the antimicrobial treatment of surfaces, is described. The compounds exhibit a pronounced action against pathogenic gram-positive and gram-negative bacteria, and also against yeasts and molds.

O uso de hydroxyphenyl-1,3-propanediones da fórmula: ## do ## STR1 wherein R.sub.1 e R.sub.2 são cada um independentemente do outro hidrogênio, C.sub.1 - alkyl C.sub.12, C.sub.1 - C.sub.12 alkoxy, trifluoro-C.sub.1 - alkyl C.sub.3, phenyl ou halogênio; R.sub.3 é uns 5- ou um radical 6-membered heteroaromatic; thiophenyl; ou um radical da fórmula: ## do ## STR2 R.sub.4, R.sub.5, R.sub.6 e R.sub.7 são cada um independentemente do outro hidrogênio, halogênio, C.sub.1 - C.sub.12 alkyl, C.sub.1 - C.sub.12 alkoxy, carboxy ou trifluoro-C.sub.1 - alkyl C.sub.3; no tratamento antimicrobial das superfícies, é descrito. Os compostos exibem uma ação pronunciada de encontro às bactérias gram-positive e gram-negative pathogenic, e também de encontro aos fermentos e aos moldes.