The species most often used for acute lethality test are the mouse and the rat. The main objective of this type of acute toxicity studies is to determine the LD₅₀, the lethal dose at which half of the test population dies in a 14-day observation following a single dose. The acute toxicity test is also typically with rodents; its focus is on acute effects and clinical signs, not on death.

The subchronic study, with the principal objective of establishing a no observed adverse effect level (Slide 9), is usually conducted in two species (rat and dog) at three doses given by the oral route daily for a period not exceeding 90 days. The high dose is typically determined from the acute lethality study, a dose supposedly high enough to produce toxicity but cause 10% fatalities or less. The low dose is a level at which no apparent toxic effects would be produced. The third dose is intermediate between the high and the low.

Chronic or long-term exposure studies are conducted essentially in the same manner as the subchronic studies are, except that the period of exposure is longer than 3 months. When carcinogenicity is also of interest, these chronic toxicity studies are performed typically in rats and mice and extend over the average lifetime of these species. These carcinogenicity studies each require 50 to 60 rats or mice per group per sex from the start to ensure that 25 to 30 animals per dose would survive the 2-year period. As in the subchronic studies, both gross and microscopic pathologic examinations are made on both the animals that have survived the chronic exposure and those that have died prematurely (along with laboratory tests performed periodically).