Hop stunt viroid (HSVd) is the viroid with the broadest host range known so far. In some hosts, such as grapevine and apricot, the infection seems to be latent. In other species, HSVd is found associated with disorders of serious economic importance e.g. hop stunt and dapple fruit in plum and peach, and citrus cachexia. A recent study (Cañizares et al., 1998) revealed the presence of HSVd in 81 % of the apricot trees tested in south-eastern Spain. By using a non-isotopic tissue printing technique we found that petiole tissue was a very good source of viroid. We then used transversal sections of infected petiole tissue to follow the presence of HSVd in apricot trees during a whole year. The results showed that viroid titter was higher from May to July, after which the accumulation level of HSVd slightly decreased. Surprisingly, by December, the viroid title had recovered levels similar to those observed in July. The significance of these results is discussed.