The gain in open probing attachment level as a result of a guided tissue regeneration procedure with Gore-Tex Periodontal Material was measured in 62 sites. The incidence of complications was evaluated. When sites with a complication were compared to those without complication, there was no statistically different gain or loss of newly regenerated tissue. However, the occurance of sloughing of the gingival flap decreased the amount of gain in open probing attachment level. Analysis of the data also revealed that the combined use of allografts and a delay in the removal of the Gore-Tex Periodontal Material had a synergistic positive effect on the gain in open probing attachment level. No association between these treatment variables and the incidence of the complications was found.