The study was concerned with measuring patterns of approach and withdrawal in four breeds of dogs; namely: beagles, wire-haired fox terriers, basenjis and Shetland sheep-dogs. Each dog was exposed to a variety of stimuli including : a black rubber snake, a bone, a life-sized head of a clown, a mirror, a live puppy, etc. Behaviors of approach or withdrawal in relation to each stimulus were rated, and in addition, contact time, gridcrossings, latency and urinations were also recorded. Marked breed and sex differences were found on almost all measures. The beagles appeared to withdraw the most and the terriers were the most active and approachful. Most of the measures were found to show high retest reliability. The data support the view that temperamental differences may be determined to a considerable degree by hereditary factors, and that multiple measures are necessary for unambiguously assessing the behavior of organisms.