The electrochemical behavior of neural implants with 50 microm-diameter platinum electrodes was tested during acute implantations in the motor cortex of anesthetized rats. Custom Ag|AgCl reference electrodes were prepared that could be co-implanted with the probes. The results obtained in vivo are compared with in vitro measurements performed in buffered saline solution (PBS) with and without the addition of bovine serum albumin (BSA). The presence of BSA clearly altered the performance of the electrodes which was studied by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), voltage transient measurements (VT) and monitoring of the open circuit potential (OCP). We found that hydrogen gas evolved at 1.22 A/cm(2) in BSA-free PBS whereas in BSA-containing PBS it occurred already at 0.51 A/cm(2).