Table 1. Incidence and Severity of Bronchial Lesions in Rats Exposed to 2,3-Pentanedione.

Bronchial Lesion	0 ppm	200 ppm
Fibrosis	0/6 a	5/5 (2.0) b
Epithelial ulceration	0/6	5/5 (1.6) c
Epithelial regeneration	0/6	5/5 (1.8)
Epithelial hyperplasia	0/6	5/5 (1.4)
Inflammation	2/6 (1.0)	5/5 (2.6)

^a Incidence of lesion / number of animals examined.

^b Fibrosis score (see Materials and Methods).

^c Severity score based upon both local severity and the extent of the lesion, using a standard

4 point scale of 1+ = minimal, 2+ = mild, 3+ = moderate, and 4+ = marked.