African wild dog (Lycaon pictus) predation was observed in Ngorongoro Crater, Tanzania, between Setp. 1964, and July, 1965, when packs were in residence. The original pack of 21 dogs remained only 4 mo., but 7 and then 6 members of the group reappeared in the Crater at irregular intervals. The ratio of males:females was disproportionately high, and the single bitch hi the small pack had a litter of 9 in which there was only one female. The pack functions primarily as a hunting unit, cooperating closely in killing and mutual defense, subordinating individual to group activity, with strong discipline during the chase and unusually amicable relations between members. A regular leader selected and ran down the prey, but there was no other sign of a rank hierarchy. Fights are very rare. A Greeting ceremony based on infantile begging functions to promote pack harmony, and appeasement behavior substitutes for aggression when dogs are competing over meat. Wild dogs hunt primarily by sight and by daylight. The pack often approaches herds of prey within several hundred yards, but the particular quarry is selected only after the chase begins. They do not run in relays as commonly supposed. The leader can overtake the fleetest game usually within 2 miles. While the others lag behind, one or two dogs maintain intervals of 100 yards or more behind the leader, in positions to intercept the quarry if it circles or begins to dodge. As soon as small prey is caught, the pack pulls it apart; large game is worried from the rear until it falls from exhaustion and shock. Of 50 kills observed, Thomson''s gazelles (Gazella thomsonii) made up 54 percent, newborn and juvenile wildebeest (Connochaetes taurinus) 36 percent, Grant''s gazelles (Gazella granti) 8 percent, and kongoni (Alcelaphus buselaphus cokei) 2 percent. The dogs hunted regularly in early and late afternoon, with a success rate per chase of over 85% and a mean time of only 25 min. between starting an activity cycle to capturing prey. Both large and small packs generally killed in each hunting cycle, so large packs make more efficient use of their prey resource. Reactions of prey species depend on the behavior of the wild dogs, and to disturbance game was far less than has been represented. Adult wildebeest and zebra (Eguus burchelli) showed little fear of the dogs. Territorial male Thomson''s gazelles, which made up 67% of the kills of this species, and females with concealed fawns, were most vulnerable. The spotted hyena (Crocuta crocuta) is a serious competitor capable of driving small packs from their kills. A minimum of 4-6 dogs is needed to function effectively as a pack. It is concluded that the wild dog is not the most wantonly destructive and disruptive African predator, that it is an interesting, valuable species now possible endangered, and should be strictly protected, particularly where the small and medium-sized antelopes have increased at an alarming rate.