Figure 1.

Incidence of squamous cell carcinoma of the nasal passages and cell proliferation in rats exposed to formaldehyde. □ shows tumor incidence (%) from the 24 month study versus formaldehyde concentration (ppm) (Kerns et al., 1983). ○ shows tumor incidence from the 24-month study (Monticello et al., 1996). ▲ shows cell proliferation (mean unit length labeling index) from the 6 month study as fold increase over control (Monticello et al., 1990). ◆ shows cell proliferation (mean unit length labeling index) from the 12 month study as fold increase over control (Monticello et al., 1990). ● shows cell proliferation (mean unit length labeling index) as fold increase over control (Monticello, Morgan, and Hurtt, 1990).