Many infections such as otitis media, sinusitis, cholesteatoma, tonsillitis and adenoiditis are caused by biofilm forming mucosal pathogens (P. aeruginosa, S. aureus, S. peneomoniae, H. influenzae and M. catarrhalis). Moreover, the role of biofilms in the chronic otolaryngologic infections has been recognized for otitis media, tonsillitis and rhinosinusitis. Finally, bacterial biofilms of S. aureus, S. epidermis and E. faecalis are the leading cause of medical device-related infections. Pathogens growing as biofilms are intrinsically resistant to conventional antibiotics and therefore the discovery of new compounds able to act against biofilm aggregated micro organisms is an urgent task. Previously, we reported the study on the antibiofilm activity of 4-diazopyrazole derivatives of type 1 against S. aureus ATCC 29213, methycillin-resistant S. aureus ATCC 43866 and methycillin-resistant S. epidermis RP626 preformed biofilms. The compounds were active at the maximum tested concentration of 25 microg/ml. On the basis of these results, we have prepared a new series of 4-diazopyrazole derivatives 2a-i and 3 which take the phenylureido or phenylacetamido moiety at 5-position of the pyrazole nucleus. The compounds has been tested preliminarly against planktonic (single cells) strains of S. aureus (ATCC 25923), S. aureus (ATCC 29213), E. coli (ATCC 25922) and P. aeruginosa (ATCC 9027), showing MIC’s values in the range 50-0.097 microg/ml. Experimental work aimed to verify the effect of the above compounds on the corresponding microbial biofilms are in progress.