In order to examine the effect of fluctuating (nonpreaveraged) hydrodynamic interaction on the hydrodynamic-radius expansion factor alpha(H) and also the viscosity-radius one alpha(eta), a Monte Carlo simulation study is made on the basis of the polymethylenelike rotational isomeric state chain in the Zimm rigid-body ensemble approximation. All the results obtained are consistent with the recent finding (by Yamakawa’s group) that the experimental values of alpha(H) are appreciably smaller than the values predicted by any available theory and rather agree with the theoretical and experimental values of alpha(eta), indicating that the effect is significant on alpha(H) but is negligibly small on alpha(eta) if any. The present results along with the recent experimental ones also confirm the validity of the quasi-two-parameter scheme for alpha(H) and alpha(eta) as well as for the gyration-radius expansion factor alpha(S); i.e., these expansion factors are functions only of the scaled excluded-volume parameter (z) over tilde defined in the Yamakawa-Stockmayer-Shimada theory of the excluded-volume effect in the Kratky-Porod wormlike chain and the helical wormlike chain.