Backgrounds: In this study, we measured monoamines and amino acids in the brain of the cynomolgus monkey using a small molecule microdialysis method. We also evaluated the migration of antibodies into the brain using the polymer microdialysis method. Methods: In the small molecule microdialysis method, probes were inserted into the nucleus accumbens and hippocampus of the brain, and probes were perfused with Ringer solution. After completion of preperfusion, dialysates were collected at 30-minute intervals, and at the final time point, the brain was stimulated with high potassium Ringer solution for 20 minutes. In the polymer microdialysis method, the dialysate was collected using the push-pull method because the cutoff value for the molecular weight of the probe is 1000 kDa. We administered trastuzumab, an antibody drug, to cynomolgus monkeys and analyzed its pharmacokinetics in plasma and brain tissue perfusate. Results: In the small molecule microdialysis method, serotonin, norepinephrine, dopamine, acetylcholine, Glutamic acid remained stable for 2.5 hours, but increased 2 or 3 times at 3 hours by high potassium stimulation. The metabolites of these monoamines and precursors of neurotransmitters were declined by high potassium stimulation. In the polymer microdialysis method, plasma concentrations of trastuzumab peaked about 1 hour after the beginning of intravenous infusion and maintained or gradually declined. In contrast, the concentrations in brain dialysate increased gradually and reached a peak at about 5 hours after the beginning of infusion.