The storage and loss shear moduli, G' and G'', have been measured for dilute solutions of paramyosin from the clam Mercenaria mercenaria in water and glycerol--water mixtures containing potassium chloride and phosphate buffer. The Birnboim--Schrag multiple-lumped resonator was used in the frequency range from 150 to 8100 Hz; the concentration range was 0.7 to 2 X 10(-3) g/mL and the temperature range was 0.0 to 6.0 degrees C. The intrinsic moduli were obtained by extrapolation to infinite dilution. When compared with predictions of Yamakawa for a rigid cylindrical molecule, they agreed at low frequencies but diverged at high frequencies. Excellent agreement was obtained with calculations for a hybrid model whose relaxation times are attributed to rigid-body end-over-end rotation together with some internal modes of motion, probably flexural. The rotational relaxation time agreed rather well with that determined by DeLaney and Krause from electrical birefringence measurements. From the ratio of the rotational to the longest flexural relaxation time, the flexural rigidity and Young's modulus of the paramyosin molecule were estimated by relations derived by Wada and collaborators; the modulus was 1.2 X 10(10) dyn/cm2.