Eight dogs at 2 and 3 years of age and weighing 11-14 kg were used. The dogs were divided into two groups. The first group was administered with enrofloxacin by intra-vitreal route at a dose of 2 mg/eye, whereas the second group was administered the same antibiotic at the same dose by subconjunctival route. Subsequent to the administration, the samples of the aqueous humour were collected at 0.083, 0.25, 0.5, 1, 2, 4, 6, 24, and 72 h. Slope factor (alpha, beta), k(a) (absorption rate constant), absorption half-life t(1/2a), half-life of elimination in the aqueous humour (t(1/2 beta)), mean residence time in the aqueous humour (MRT), area under the concentration time curve from zero up to infinity (AUCO(0 ->infinity)), maximal concentration in the aqueous humour after subconjunctival administration (C-max), and time needed to reach C-max(t(max)) values were assessed by means of pharmacokinetic analyses. Accordingly, a statistically significant difference was demonstrated between groups in t(1/2 beta), MRT, and AUCO(0 ->infinity) values. No statistically significant difference was observed between groups with respect to the other parameters. In conclusion, the administration of enrofloxacin by intra-vitreal route was considered to be a rapid and effective method for the treatment of intra-ocular infections than subconjunctival application. After intra-vitreal drug application, t(1/2 beta), MRT, and AUCO(0 ->infinity) were 9.47 +/- 3.79 h, 7.77 +/- 2.10 h, and 202.18 +/- 41.80 mu g/h/mL, respectively, while after subconjunctival application these values were 3.84 +/- 1.30 h, 4.75 +/- 1.11 h, and 10.29 +/- 8.76 mu g/h/mL.