The effects of nitrogen ion implantation of Ti-6AI-4V alloy on growth of Pseudomonas aeruginosa bacteria on surfaces of the alloy have been investigated. Results for ion implanted samples were compared with controls with similarly smoothly polished surfaces and with controls that had intentionally roughened surfaces. The test consisted of exposing sterile alloy samples to a microbiological broth, to which 24 hour-old cultures of Pseudomonas aeruginosa had been added. After bioassociation at normal temperature 37°C, bacteria adhering to the surface were fixed and treated with a new ruthenium tetroxide staining method, and quantified by use of scanning electron microscopy (SEM), back-scattered electron imaging and EDAX energy dispersive microanalysis. For smooth samples of the alloy, after a 12 hour growth period, the retained bacteria (revealed by the biologically incorporated ruthenium), decreased monotonically with nitrogen dose out to a total fluence of approximately 7 × 1017/cm2 in an affected depth of approximately 0.1500 μm. The SEM confirmed that the Pseudomonas aeruginosa adhered equally to control materials. The ruthenium studies revealed that the amount of bacterial adhesion is indirectly proportional to the nitrogen ion implantation of the titanium. The greater the percentage of nitrogen ion implantation in the titanium alloy, the less bacteria colonized the disk.