The objective of the present real-time in vivo experiment was to assess guided bone regeneration (GBR) in standardized calvarial defects using particulate graft material (Bio-Oss) and β-tricalcium phosphate (β-TCP) with adjunct recombinant human platelet-derived growth factor (rhPDGF) therapy. Eighteen female Sprague-Dawley rats with a mean age and weight of 8 ± 0.53 weeks and 250 ± 0.49 g, respectively, were used. Following surgical exposure, a full-thickness standardized calvarial defect was created on the parietal bone using a trephine drill with an outer diameter of 4.6 mm. For treatment, rats were randomly divided into three groups (six rats per group): (1) control; (2) rhPDGF + Bio-Oss, and (3) rhPDGF + β-TCP. Volume of newly formed bone (NFB), bone mineral density (BMD) of NFB, volume of remnant bone particles, and BMD of remnant bone particles were assessed using in vivo microcomputed tomography. Measurements were made at baseline and at 2, 4, 6, and 10 weeks after the surgical procedures. At 10 weeks, all animals were sacrificed and calvarial tissues were assessed histologically. In the control group, a significant increase in BMD of NFB was observed at 6 weeks (mean ± standard deviation [SD], 0.32 ± 0.002 g/mm3) (P .01) from baseline, and the defect did not regenerate completely. In the rhPDGF + Bio-Oss group, mean ± SD volume (2.40 ± 0.25 mm3) (P .01) and BMD (0.13 ± 0.01 g/mm3) of NFB significantly increased at 4 weeks and 6 weeks, respectively, from baseline (P .001). In the rhPDGF + β-TCP group, mean ± SD volume (2.01 ± 0.7 mm3) and BMD (0.12 ± 0.02 g/mm3) of NFB significantly increased at 4 weeks from baseline (P .01). In the rhPDGF + Bio-Oss and rhPDGF + β-TCP groups, mean ± SD BMD of remnant bone particles (0.31 ± 0.11 g/mm3 and 0.23 ± 0.01 g/mm3) showed significant reduction at 6 and 10 weeks, respectively, compared with baseline values (1.12 ± 0.06 g/mm3 and 0.92 ± 0.01 g/mm3, respectively) (P .001). Histologic results at 10 weeks showed NBF in the rhPDGF + Bio-Oss and rhPDGF + β-TCP groups. In real time assessment, when rhPDGF was added to β-TCP, BMD and bone hardness significantly increased compared with the other two groups.