Proliferation of SCC-25 cells was increased by HPV16 and decreased by HPV18 and co-transfection, in vitro. HPV-transfected and control SCC-25 cells were plated in 96-well assay plates with media containing 10% FBS and allowed to proliferate for three days. (A) HPV16-transfected cell proliferation was significantly enhanced, while HPV18- and HPV16/18-cell proliferation was slightly inhibited, compared with control cells (n = 96, p < 0.05). (B) The relative change in proliferation as measured between day 3 and day 1 revealed that baseline SCC-25 proliferation of 2.-fold was increased to approximately 3-fold by HPV16, while HPV18 and HPV16/18 reduced this rate to approximately 1- and 1.5-fold, respectively. (C) Two-tailed t-tests and ANOVA revealed that only HPV16-transfected SCC-25 cells were statistically different from controls.