INTRODUCTION: Multielectrode silicon probes can record neuronal signals with combination of spatial and temporal resolution that other recording techniques cannot provide. Here we propose a novel microelectronic system that combines this functionality with advanced electrical stimulation. AIM(S): We designed a modular system for multielectrode electrical stimulation and recording in the brain of a living animal. It can be combined with any silicon probe used for brain research. It can generate complex sequences of stimulation pulses and simultaneously record at up to 512 electrodes. It can use up to 4 silicon probes in parallel, providing bidirectional communication with populations of neurons simultaneously in several brain areas. METHOD(S): The system is based on a dedicated multichannel CMOS chip. The chip includes 64 channels, digital circuitry for real-time communication with the control computer and a multiplexer that sends amplified signals from 64 electrodes into a single output line. The amplifier gain can be changed from 110 to 550. The low cut‑off frequency is set between 200 mHz and 3 Hz, the anti-aliasing filter is set at 7 kHz and the sampling rate is 40 kHz. The stimulation signal is controlled independently for each channel with 12-bit resolution and refresh rate of 40 kHz. Each amplifier can be disconnected from the electrode for the duration of the stimulation pulse for the artifact reduction. Up to 8 chips can be controlled in parallel with dedicated LabView software. RESULTS: Base version of the system was produced and tested with positive results. The final system is in the integration phase. We plan the first experiments to take place in the fall 2017 at the Nencki Institute for Experimental Biology. CONCLUSIONS: The reported system can generate complex sequences of stimulation pulses and record neuronal signals with very low artifacts at 512 electrodes, making it a powerful tool for mapping of the functional connections between brain circuits. FINANCIAL SUPPORT: Grant 2013/08/W/NZ4/00691, Polish National Science Centre.