Rapid, sensitive and specific diagnostic methods are needed to confirm freedom of stocks from key pathogens before the release of stocks. Of 19 tissue culture laboratories in the UK and elsewhere in Europe, 16 recorded losses due to Botrytis cinerea and 6 recorded Pythium and Rhizoctonia as problems. The role of RH in fungal pathogenesis and problems in the measure and control of RH are discussed. The possible detection of downy mildew of micropropagated Rubus and Rosa caused by Peronospora rubi (P. sparsa) using polymerase chain reaction techniques is discussed.