Intrinsic viscosity, [eta] weight average molecular weight, M omega, relationships are reported for narrow molecular weight distribution linear polyisoprene and polystyrene samples in CCI4 at 25 degrees C. Molecular weight values cover a range nearly two orders in magnitude, extending as low as 3 X 10(3). In the case of polystyrene there exists a molecular weight range (around M omega = 16,700) corresponding to a change in the Mark-Houwink-Sakurada (MHS) exponent from alpha = 0.71 to alpha = 0.54. Comparisons between the viscometric and hydrodynamic radii, from literature data, are made. For polyisoprene the MI-IS relationship is reported in CCl4, for the first time. For this case alpha = 0.713 for the whole range of molecular weights studied. Values for the second virial coefficient from low-angle light-scattering measurements support the conclusions drawn from viscometry that CCl4 is a good solvent for both polymers studied. The different behavior of the MHS exponent may be attributed to the difference in chain flexibility.