Previous studies have shown that ultrasonic backscattering from red blood cells suspended in saline is proportional to the fourth power of frequency for frequencies below 15 MHz, as predicted by Rayleigh scattering theory. Recently, we have extended the measurements up to 30 MHz, because scattering of ultrasound by red blood cells may no longer be negligible at these frequencies and can affect, to a great degree, the operation of intravascular imaging devices. The experimental results show that the fourth power dependence on frequency of the backscattering coefficient for porcine erythrocytes suspended in saline solution appears to be valid up to 30 MHz. To confirm this, backscattering cross-section of porcine red cells was computed as a function of frequency using the T-matrix method. Since at higher frequencies the shape of the scatterers may also play a significant role, its effect was investigated by treating the red cell as a sphere, a disc, and a biconcave disc of the same volume. Good agreement was obtained between the experimental and theoretical results.