Particles of BaSO4 with sizes in nano-scale and micro-scale ranges were investigated for their interactions with fibroblasts in order to determine the biocompatibility of nano-sized particles. Cells were incubated in the presence of particles at 1, 10 and 100 times the particle to cell surface area ratio and at a single concentration of 0.138 mg/ml. Production by the fibroblasts of an inflammatory cytokine in response to the particles was measured and the effect of particle size and volume on cell viability was examined. All particles were cell associated and some agglomeration was visible at all size ranges. Release of interleukin-6 by cells subjected to the same concentration of Ba SO4was similar to control levels, while addition of 1x surface area ratio (SAR) of particles to cells resulted in an increase in IL-6 from 94 pg/ml for 100 nm particles to 218 pg/ml with 2 μm particle diameter. By increasing particle to cell surface area ratios from 1× to 100x, cell viability was compromised for the 2μm particles but was not affected by the nanometer sized BaSO4 particles.