A comparison was made of methods for viroid detection. Molecular hybridization using cDNA is a very sensitive method that can handle large quantities of samples at the same time but it has the disadvantage that only small amounts of the sample can be applied to the nitrocellulose filter. The method therefore can only detect viroid in plants when its concentration is 10–20 ng g‐1of leaves, using32P as a marker system. Bi‐directional electrophoresis can detect viroid in plants when its concentration is 10 ng g‐1of leaves, because it uses larger samples. It does not need hazardous chemicals like32P and formamide, and the reading of the results of the test is less liable to failures because it is based on two criteria (position and intensity of RNA band). The Dutch Plant Protection Service and the Dutch General Inspection Service for Ornamentals therefore use a modified bi‐directional electrophoresis method to detect potato spindle tuber viroid and chrysanthemum stunt viroid, res