The following dosages were performed on the given number of males/females, for the duration of 6 hrs/day, 5 days/week, for 4 weeks. m(3) means m to the 3rd power. Exposure of rats to KF-995 at a level of 2000 mg/m(3) air resulted in a number of slightly reversible adverse effects. Slight leucocytic infiltrations were observed in the lungs of both males and females at the end of the exposure period. At the end of the observation period this change was found in the lungs of only one female of the high-dose group. The increased liver weights in both sexes were not accompanied by histopathological changes in this organ. The low bilirubin values in males might support the assumption that the liver was effected. The decrease in ALP value in males at the end of the recovery period could not be associated with any other lesions. Though it cannot be excluded that this low value is a delayed effect related to the exposure, it is more likely that it was a causal finding unrelated to treatment. The reversible decrease in red blood cell counts in relation to enlargement of the mean erythrocyte volume (MCV) and the decrease in haemoglobin concentration of the erythrocytes (MCHC) in males of the high dose group were considered being indicative for a recovering anaemia. Another hematological parameter effected was the white blood cell counts in males of this group. The increase of the numbers was mainly caused by an increase of the number of neutrophils. This finding also appeared to be reversible since it was not found in males of the recovery period. The relatively high creatinine level in females at the end of the exposure period was neither accompanied by changed urine parameters nor by histopathological changes in the kidneys. Therefore, this high creatinine level was considered a causal finding. At a level of 400 mg KF995/m(3) air there was an increase in white blood cells and neutrophil counts in males. Since these changes were observed also in males of the high dose group and in addition there was a dose effect relationship, it was considered an exposure related effect. From the results of the present study it is concluded that under conditions of the present study the no-adverse effect level of KF995 is 80 mg/m(3) air in rats.