The results of microbiological research carried out on haematological patients admitted to the same ward are reported. The pathogenic flora observed consisted mainly of gram-negative germs (60%). Pseudomonas infections represented the most important problem because of their frequency and the consequent clinical problems. The in vitro sensitivity of 306 strains of gram-negative germs to 11 different antibiotics has been analysed. Amikacin proved to be easily the most effective antibiotic against isolated pathogens.