Proliferation of CAL27 cells was increased by both HPV18 and HPV16 in vitro. HPV-transfected and control CAL27 cells were plated in 96-well assay plates with media containing 10% fetal bovine serum (FBS) and were allowed to proliferate for three days. (A) The addition of HPV16 and HPV18, either alone or in combination, was sufficient to stimulate the proliferation of CAL27 cells significantly (n = 96, p < 0.01). (B) Measurements of the relative change in proliferation between day 3 and day 1 revealed that the addition of HPV stimulated an increase in CAL27 proliferation from 1.3-fold to nearly 2.0-fold under each experimental condition. (C) Statistical tests between non-transfected and transfected cells revealed that the HPV-induced increases in proliferation were significant, verified using two-tailed t-tests and ANOVA.