The second viral coefficient A(2) was determined for isotactic poly(methyl methacrylate) (i-PMMA) over a wide range of weight-average molecular weight M(W) from 7.89 x 10(2) to 1.93 x 10(6) in acetone at 25.0 degrees C, for M(W) greater than or equal to 1.55 x 10(5) in chloroform at 25.0 degrees C and in nitroethane at 30.0 degrees C, and for M(W) = 6.88 x 10(5) in acetonitrile at 35.0, 45.0, and 55.0 degrees C. (Some of the data had already been obtained in the previous work.) It is shown that the observed dependence of A(2) on M(W) in the oligomer region may be quantitatively explained by the Yamakawa theory that takes account of the effect of chain ends, The values of the effective excess binary-cluster integrals beta(1) and beta(2) associated with the chain End beads are then found to be 66 and 360 Angstrom(3), respectively, in acetone at 25.0 degrees C by taking the repeat unit as a single bead. The analysis shows that the effect of chain ends remains even for relatively large M(W) in the good solvent as in the cases of atactic polystyrene (a-PS) and atactic poly(methyl methacrylate) (a-PMMA). The results for the true interpenetration function Psi in A(2) without the effect of chain ends indicate that the two-parameter theory breaks down completely, as found previously for a-PS and a-PMMA; the observed Psi as a function of the cubed gyration-radius expansion factor alpha(s)(3) depends separately on M(W) and on the reduced excluded-volume strength lambda B. It is found that the values of Psi for i-PMMA are appreciably smaller than those for a-PMMA in the same solvent, i.e., for the same value of the binary-cluster integral beta, while the former values almost coincide with the latter for the same lambda B. The Yamakawa theory that takes account of the effects of chain stiffness and local chain conformation on the basis of the helical wormlike chain may explain satisfactorily the observed behavior of Psi and also the remarkable difference in it between i-PMMA and a-PMMA, the effects appearing in Psi through both lambda B and the mean-square radius of gyration [S-2].