A double-blind investigation comparing a control dentifrice with one containing active ingredients was conducted to determine their effect on dentinal hypersensitivity in 67 human subjects. Baseline data was obtained by patient questionnaire, dental examination and by soliciting subjective responses to controlled mechanical and thermal stimuli. A calcium carbonate-based toothpaste constituted the base for both the control and active dentifrice. The active dentifrice contained 0.8% sodium monofluorophosphate and 1.3% formalin while the control lacked these ingredients. Dentifrices were supplied to patients on a random basis, and patients were instructed to brush twice each day for 28 days. Mechanical and thermal response as accomplished at baseline were obtained at 14 and 28 days after baseline on 60 subjects. A statistically significant reduction was not obtained in response to mechanical stimulus. The active dentifrice demonstrated a statistically significant reduction (P less than 0.05) to thermal stimulus at both 14 and 28 days.