Grapevine fanleaf virus (GFLV) is one of the most destructive and wide-spread viral diseases affecting grapevine (Bovey et al. 1980). Since virus disease control with conventional methods is very difficult, major efforts are made towards resistance breeding. Coat-protein-mediated resistance (CPmR) has demonstrated to confer a high level of resistance in herbaceous model plants (Beachy et al. 1990; Pacot-Hiriat et al. 1999) and is a promising strategy to obtain virus-resistance in perennial plants like grapevine using a pathogen derived gene. In order to produce resistant grapevines not only an efficient protection, but also environmental safety aspects have to be considered (Gölles et al. 2000). The main purpose of this work is to answer the question whether truncated coat proteins maintain the capacity of self-assembly, i.e. if empty capsids occur in transgenic plants. For this approach ISEM was chosen as the method of analysis, because of its direct and rapid results. It could be clearly demonstrated that ISEM is a suitable method for VLP detection in CP-transgenic grapevines and that it could be recommended as a continuous standard monitoring technique for field experiments.