Here we report the first successful physiological tests of two different wireless integrated neural interface (INI) circuits that are capable of either recording (INI5) or evoking (INIS1) neural activity via 100-channel Utah Slanted Electrode Arrays (USEAs) or Utah Electrode Arrays. Such wireless devices may offer multiple benefits for restoring neural function by reducing wire breakage, electrical noise, and the risk of infection associated with transcutaneous connections. INI5 is a low-power integrated circuit that amplifies 100 neural signals, detects spikes with programmable threshold-crossing circuits, and returns these data via digital radio telemetry. The chip receives power, clock, and command signals through a coil-to-coil inductive link. Because INI5 has not yet been fully integrated with the array, we connected the chip to a conventional USEA implanted in sciatic nerve of anesthetized cat. INI5 successfully recorded and transmitted action potentials, performed accurate on-chip spike detection at multiple user-selected threshold levels, and transmitted spike-detection data, all under completely wireless operation (power, data transmission, and command transmission). Spike firing rates and spike detections were highly correlated with stimulation (e.g., paw squeeze). We also tested a complementary chip, INIS1, for wireless neural stimulation. The chip can independently drive 100 electrodes with constant-current pulses of programmable amplitude, duration, interphasic delay, and repetition rate. INIS1 successfully and selectively activated motor nerve fibers on all tested USEA electrodes (n = 10), evoking observable motor responses and compound action potentials in hindlimb muscles. Both pulse-amplitude and pulse-width modulation produced systematic input-output curves. INIS1 also directly activated sensory fibers, evoking short-latency potentials over somatosensory cortex that survived distal nerve cut, indicating that INIS1 may be able to provide tactile or proprioceptive sensations. Finally, a fully integrated system, using an earlier (not fully functional) chip, array, power coil, and coatings, survived pneumatic insertion into sciatic nerve, and operated in vivo under wireless power at an intercoil distance of > 15 mm. Wireless INIs are becoming a reality.