The incidence of resistance to gentamicin, tobramycin, amikacin and netilmicin was determined by the microdilution method in Mueller-Hinton broth among blood culture isolates consecutively collected in 37 laboratories in 14 European countries. The distribution of bacteria was similar in each laboratory, Escherichia coli and staphylococci predominating. Resistance levels varied between laboratories but they were higher to all four antibiotics in Southern Europe than in Central and Northern Europe. Aminoglycoside resistance was usually associated with production of aminoglycoside-modifying enzymes, ANT(2″), AAC (3)-V, AAC (6′)-I predominating in Gram-negative bacilli and APH (2″)+ AAC (6′) and ANT (4′)-I in staphylococci. © 1990 by The British Society for Antimicrobial Chemotherapy.