A method is described which allows simultaneous recording of the activity of several neurons in the visual cortex of awake unrestrained kittens for a period sufficiently long to follow experience-dependent changes in receptive field properties. The electrodes consisted of 25 microns thick Teflon-coated platinum-iridium wires whose tips were tapered and coated with platinum black. They were implanted individually into the striate cortex and fixed with tissue glue to the pia mater. The other end of the electrodes was connected to a 21-pin plug and fixed to the skull in a way which allowed the wires to follow freely any movements of the brain. With this arrangement single and multi unit activity could be recorded from up to 10 sites over several weeks. In fortuitous cases the activity of a single cell could be followed over several days. The receptive field properties of these neurons were determined in awake animals by computing response histograms to moving gratings that covered the whole visual field and whose orientation could be changed in small steps. Comparison with receptive field properties that were determined for the same neurons after the kittens had been lightly anesthetized, revealed that this method allowed reliable determination of the eye preference of the neurons as well as of their orientation and direction selectivity. Since this method allowed repeated non-invasive measurements of neuronal response properties in only lightly restrained kittens, it was possible to study, in individual units, the nature and time course of changes in receptive field properties such as result from monocular deprivation and reverse occlusion.