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An earth-boring bit comprises a bit body bit body in which are mounted a plurality of cutting structures inserts, wherein at least a portion of the cutting structures comprise diamond--impregnated inserts having a total thermal exposure of less than 25 minutes above 1500.degree.F. The diamonds can be natural or synthetic diamond. The bit body itself may be diamond-impregnated, in which case it is preferred that the diamonds in the inserts make up at least 40% of the total diamond in the bit.