It is well-known that mechanical point impedance data obtained with impedance heads suffer from three types of systematic errors originating from the force crystal compliance, the mass in front of the force crystal, and the acceleration crystal compliance. Error functions have been proposed which show good correspondence with experimental data obtained with the Briiel and Kjaer impedance head B&K 8001. By using the proposed error functions to correct the estimated magnitude and phase data obtained with impedance heads, accurate results can be obtained for a wide range of load impedances. The lower magnitude limit of the apparent mass (force/acceleration) of a load to be measured by the impedance head B&K 8001, with an accuracy better than 15%, is approximately 0•0005 Ns 2/m. This limit is determined by the accuracy of the cancellation of the mass in front of the force crystal. The upper magnitude limit of the apparent mass of a load to be accurately measured is strongly frequency dependent and primarily determined by the product of frequency, force crystal compliance, and load impedance magnitudes. This limit originates from the shunt of acceleration through the force crystal compliance. For pure load masses of 50 and 1500 g, the upper 10% frequency magnitude limits are approximately 3•3 kHz and 620 Hz, respectively. The acceleration crystal compliance gives magnitudes of estimated acceleration which are generally 3% and 10% too low at 5•7 kHz and 10 kHz, respectively. This error is independent of the load impedance. The phase errors from the three error mechanisms mentioned above are also determined by the corresponding error functions, but their influence on the impedance data is generally small. Correction procedures can be performed automatically with a two-channel FFr analyzer with access to a memory and capable of performing arithmetic operations.