We have measured the ultrasonic attenuation parameters α0andnof several biological fluidsinvitroin the frequency range 2.8–6.8 MHz, using frequency shift and/or a sinc (⋅) sidelobe ratio technique. The parameters α0andndescribe the frequency‐dependent attenuation via a power‐law model, i.e., α( f)=α0 f n, wherefis frequency. The samples investigated were blood, pus, cyst fluid, bile, and infected hematoma. It was found that the values of α0span approximately the range between 0.03–0.3 dB cm−1MHz−n, and values ofnrange from about 1.1–1.3.