Low-level laser therapy (LLLT) has been reported to improve tissue healing and might therefore be useful in dental pulp capping after trauma. We evaluated the effects of a low-level diode laser (λ = 680 nm) and dental pulp-capping substances on cell proliferation. Calcium hydroxide and adhesive resin were applied as conditioned media to cultures. Half of the samples received irradiation with the diode laser at a fluence of 4 J/cm² for 60 s. Using a hemocytometer, cells were counted at 1, 3, 5, and 7 days, and the data were analyzed by ANOVA. All cultures exhibited continuous growth, except those treated with adhesive resin. As compared to the other two groups, cell proliferation was significantly lower in cultures treated with adhesive resin; it was also significantly lower in cultures treated with calcium hydroxide, as compared to the control group. When combined with dental pulp-capping materials, LLLT had no effect on L-929 cell proliferation. (J Oral Sci 52, 33-38, 2010)