We modified a wireless system to measure hippocampal neural activity in pigs, and tested a handmade microdrive for adjusting the tip of the electrode. Under general anesthesia with halothane inhalation we stereotaxically placed tungsten electrodes (5 MΩ) fitted with handmade microdrives in the temporal hippocampus of male Landrace piglets, and fixed a high-input-resistance transmitter (10 MΩ; 1000-fold amplification) to the skull. Oscillation and saturation were evident in the recording system for several days after surgery. When these phenomena ceased, we successfully recorded the hippocampal electrical activity in four of eight piglets. At 5 or 6 days following surgery, hippocampal electrical activity ?0.15 mV in amplitude was observed in resting piglets during the daytime. In this recording, delta (1.0-3.9 Hz) and theta (4.0-7.9 Hz) waves with large amplitude were frequently predominant. However, these activities often alternated with high-frequency and low-amplitude activity, even while piglets were lying down. Manipulation of the microdrive enabled us to reposition the electrodes in the hippocampus 1 week after surgery. This technical development maintains the electrode within the hippocampus to enable neuronal activity with behavioral correlates to be determined in unrestrained piglets.