To determine principles of sensory coding of spatial information on the skin, how single neurons in primary somatosensory cortex (SI) of alert rhesus monkeys [Macaca mulatta] integrate information from multiple points on the skin was examined. Recordings were made from 1091 neurons in the arm area of SI; 150 of these were studied with air puffs. Brief air-puff stimuli were applied either at single points or simultaneously at 3 points spaced 15 mm apart along the longitudinal axis of the forearm. Response profiles of the number of spikes per stimulus as a function of stimulus position within the receptive field were constructed by presenting single and triple stimuli at many locations on the skin. The profiles were used to determine the presumed spatial distribution of activity within SI cortex generated by each stimulus. SI neurons in alert monkeys were far more responsive to mechanical stimuli than those in anesthetized preparations. Unlike primary afferent fibers, cortical neurons do not resolve 3-point simultaneous stimuli presented 15 mm apart within the receptive field. This neural representation provides a possible neuronal basis of funneled sensations produced by these stimuli in humans. Three-point stimuli evoked activity in a broader population of neurons than did single-point stimuli of the same intensity. Peak responses to 3 air puffs were no different from maximum responses to single air puffs in 74% of the neurons studied in detail, suggesting saturation of excitatory convergent input from the individual stimulus sites. Stimulus intensity may be coded by the integrated activity of the entire population, rather than simply by the most active cells representing the field center. When 3 air puffs were presented with the lateral one placed over the center, 45% of the neurons showed significantly smaller responses to 3-point stimuli (P < 0.05), and only 2% showed summated responses, suggesting a lateral inhibitory interaction. In the periphery of the field, cortical responses mimicked those of the air puff closest to the field center, or were smaller. Summation of excitation from simultaneously applied multiple-point stimuli occurred only when at least 2 stimuli were close to the field center and spanned it. This restriction of summation to the region immediately surrounding the field center suggests that more widely spaced stimuli might be resolved as separate points. Two-point discrimination thresholds may not depend on the diameter of cortical receptive fields, but only on the size of the subregion in which summation occurs.