Although commercially-available poly(methyl methacrylate) bone cement is widely used in total joint replacements, it has many shortcomings, a major one being that it does not osseointegrate with the contiguous structures. We report on the in vitro evaluation of the biocompatibility of modified formulations of the cement in which a high loading of hydroxyapatite (67 wt/wt%), an extra amount of benzoyl peroxide, and either 0.1 wt/wt% functionalized carbon nanotubes or 0.5 wt/wt% graphene oxide was added to the cement powder and an extra amount of dimethyl-p-toluidiene was added to the cement's liquid monomer. This evaluation was done using mouse L929 fibroblasts and human Saos-2 osteoblasts. For each combination of cement formulation and cell type, there was high cell viability, low apoptosis, and extensive spread on disc surfaces. Thus, these two cement formulations may have potential for use in the clinical setting.