Acute toxicity was determined in 28 male albino Harlan Wistar rats receiving resin grade RG 244 UCC calidria asbestos as a 1% (w/v) suspension in 0.85% saline by tracheal instillation. A total of 1 ml of the solution was received by 13 rats and 0.5 ml was received by 15 rats. There were no mortalities or clinical observations reported. Gross and microhistopathological examinations were made on the lungs, liver, kidneys, heart, spleen, adrenal, thyroid, parathyroid, trachea and esophagus. Histopathological examinations of the lungs at 30 days post-testing revealed granulation tissue, thickened stroma and an accumulation of giant cells. Examination after 60 days revealed inflammation and ingrowth of connective tissue causing blockage of a terminal bronchus, atelectasis (collapse) of lung lobes and fibrotic foreign body nodules. After 90 days, examination revealed chronic foreign body pneumonia, emphysema, chronic inflammatory cell foci, dilated bronchioles and lung hemorrhage. Examination at 180 days revealed decrease in the normal lung tissue, pink hyalin material and bluish homogeneous material. Document includes: The Fibrogenic Potential of Asbestos Products Via Intraperitoneal Injection in Guinea Pigs, Rats, and Rabbits and by the Intratracheal Route in the Rat.