A description is given of three near-field methods of measuring the amplitude attenuation and velocity of longitudinal ultrasound in fluids. The methods, all using simple commercial apparatus, are based on interferometric (continuous wave), tone-burst (a short harmonic wave) and pulse techniques. They are all compared by making measurements on a reference silicone fluid, with excellent agreement within the experimental uncertainties of approximately +or-0.5% in velocity and approximately +or-3% in attenuation. Furthermore, agreement is found within these uncertainties with far-field ultrasonic data obtained from a far-field technique for the same fluid. The particular advantages of each method are discussed and applications are demonstrated to measurements in colloidal suspensions of rigid and swelling colloidal particles. The swelling of bentonite clays is monitored by time-dependent changes in the attenuation and velocity and a comparison is made with similar changes which are commonly measured rheologically at much lower frequencies.