Since the topic of microplastics and the detection of these small plastic particles is becoming increasingly important in science, it is necessary to establish methods that allow for a non-destructive detection of microplastics in research objects. Especially with respect to the detection of environmentally relevant concentrations of microplastics in experimental organisms without destroying their body structures X-ray micro-computed tomography (μCT) is a very promising technique. We report first results of experiments with radiopaque polyurethane microplastics. Ten terrestrial and aquatic invertebrate species were selected as experimental organisms to provide a cross-section of different invertebrate taxa. In nine of the ten organisms used, microplastic particles could be easily detected by μCT, and in most cases the exact position of the plastic in the digestive tract of the individual organisms could also be determined. In animals with a solid cuticle, the method is also well suited for detecting external structures. In order to be able to make more precise statements about the position of the microplastics in the body structure of the animals radio-opaque staining methods are available and have to be tested in future studies. The method described here is particularly suitable for non-destructive detection of microplastics in organisms at low natural microplastic concentrations in experiments on the uptake and trophic transfer of microplastics.