A thermophilic bacterium, identified as a neighboring species to Geobacillus thermocatenulatus, having a growth optimum at 55 degreesC and, capable of degrading nylon 12, was isolated from soil by enrichment culture technique at 60 degreesC. At this temperature, the strain grew on 5 g nylon 12 l(-1) with a decrease in its molecular weight from 41 000 to 11 000 over 20 d. The degradation was assumed to be due to endogenous hydrolysis of amide bond in nylon 12. The strain degraded also nylon 66 with a decrease in its molecular weight from 43 000 to 17 000 in 20 d at 60 degreesC. Nylon 6 was not degraded.