The aac(6')-Ik gene which confers resistance to aminoglycosides in Acinetobacter sp. 6 CIP A165 was characterized. The resistance gene was identified as a coding sequence of 438 bases pairs corresponding to a protein with a calculated mass of 16627 Da. Alignment of aac(6')-Ik with aac(6')-Ig from Acinetobacter haemolyticus indicated 83% identity. Like aac(6')-Ig of A. haemolyticus and aac(6')-Ij of Acinetobacter sp. 13, the aac(6')-Ik gene was apparently located in the chromosome and was species specific. The high degree of identity between aac(6')-Ig and -Ik, compared with genomic DNA relationships between the host species, indicated that these genes have diverged from a common ancestor in a parental Acinetobacter species.