Abstract
By use of a superspace generalization of the involution technique (method of image), it is shown that dilaton tadpole amplitudes for the world sheets with the topologies of disk and projective plane cancel for the SO(32) type-I superstring. The same method also shows that the amplitudes at the one-loop level, i.e., on the torus, cylinder, Möbius strip, and Klein bottle, vanish after summation over spin structures. The results suggest that the theory is finite up to two loops.