The open field was introduced by Calvin Hall in 1934 as a means for assessing emotionality in a novel environment. Since its introduction, it has become one of the most widely used test pro cedures in comparative psychology. A review of the literature identified more than 2,000 references to the device since 1974. Although Hall first used the open field with rats, it was used with mice by Tobach and Schneirla in 1962, with hamsters by Tobach and Gold in 1962, with guinea pigs by Tobach and Gold in 1966, and with squirrel monkeys, cats, rats, house mice, and chickens by Candland and Nagy in 1969. It has since been used with virtually every species studied by comparative psychologists (e.g., voles-Turner, Iverson 8c Severson, 1983; spi ders-Baatrup 8c Baylay, 1993; rhesus mon keys-Ferguson, Medina 8c Bowman, 1993; zebra finches-Rifa, Alonso, Ortega 8c Naranjo, 1992; paradise fish-Mikosi, Topal 8c Casanyi, 1992; domestic cattle-Boivin, le-Neindre, Chupin 8c Garel, 1992; chickens-Jones, 1987).