Fused filament fabrication (FFF) with the use of metal-polymer filaments offers a cost-effective solution in additively manufacturing metal parts. Nevertheless, the quality and dimensional characteristics of the FFF produced parts needs to be assured. This short communication reports results and findings from an ongoing investigation on the use of immersion ultrasonic testing (IUT) for the detection of defects in FFF metal parts. In this work, the BASF Ultrafuse 316L material was used with an FFF 3D printer to produce a test specimen for IUT inspection. Two types of artificially induced defects were examined: drilling holes and machining defects. The obtained inspection results are promising in terms of the capability of the IUT method to detect and measure the defects. It was found that the quality of obtained IUT images is not only probe frequency dependent but also sensitive to the part characteristics, indicating a need for a wider range of frequencies and more accurate calibration of the system for this material.