The alternating current resistance and capacity of suspensions of unfertilized and fertilized eggs of Arbacia punctulata have been measured at frequencies from 10(3) to 1.64 x 10(7) cycles per second. The unfertilized egg has a static plasma membrane capacity of 0.73 microf./cm.(2) which is practically independent of frequency. The fertilized egg has a static membrane capacity of 3.1 microf./cm.(2) at low frequencies which decreases to a value of 0.55 microf./cm.(2) at high frequencies. The decrease follows closely the relaxation dispersion of the dielectric constant if the dissipation of such a system is ignored. It is considered more probable that the effect is due to a fertilization membrane of 3.1 microf./cm.(2) capacity lifted 1.5 micro. from the plasma membrane, the interspace having the conductivity of sea water. The suspensions show a frequency-dependent capacity at low frequencies which may be attributable to surface conductance. The equivalent low frequency internal specific resistance of both the unfertilized and fertilized egg is about 186 ohm cm. or about 6 times that of sea water, while the high frequency data extrapolate to a value of about 4 times sea water. There is evidence at the highest frequencies that the current is penetrating the nucleus and other materials in the cytoplasm. If this effect were entirely due to the nucleus it would lead to a very approximate value of 0.1 microf./cm.(2) for the capacity of the nuclear membrane. The measurements do not indicate any change in this effect on fertilization.