The stability of the laser bonded titanium coated glass/polyimide microjoints were studied in vivo by implanting on a rat brain surface for 10 days. In the current state, the strength of the joints were measured by a specially designed instrument called ‘‘pressure test’’ equipment where the samples were subjected to a variable pressure load (using high pressure nitrogen) controlled by a pressure regulator. The strength of the joints seems to degrade by about 28% as a result of soaking in rat brain. The bond degradation in rat brain implants is similar compared with those soaked in artificial cerebrospinal fluid (CSF) solution. Polyimide uptakes water through existing pores in it and also water gets in the joint region through the edges of the samples. Water might have caused oxidation of the chemical bonds which are thought to have formed by the laser fabrication process. A separate set of samples were created using same parameters for testing the hermeticity of the laser bonds. The samples were also exposed to rat brain CSF and were tested for hermiticity at the end of 10 days exposure time. It was observed that the implanted samples retained their hermeticity although the bondstrength degraded by about 28%. ' 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 90B: 614–620, 2009