RNAs of the most recent foot-and-mouth disease virus isolated in Spain (A5Sp86) during the 1986 outbreak, and of the three vaccine strains in use at that time in that country, have been compared. Although these viruses are serologically indistinguishable, differences have been found among them by T1 fingerprinting. This genetic heterogeneity affects the immunogenic VP1 gene, with amino acid changes located at the carboxyterminal end of the molecule. VP1-coding sequences obtained have been compared with those previously reported for European A5 FMDVs and it has been possible to trace their phylogenetic origin. The most parsimonious evolutionary tree obtained shows that the viruses analyzed are closely related to those previously isolated in 1983 in Spain, Portugal and Morocco. In spite of the VP1 sequence homology shown by this group of viruses, the genetic distances among field isolates and vaccine strains are significantly shorter than the distances found among field isolates. Thus, a significant relationship among virus recovered from recent outbreaks and the vaccine strains in use at that time in Spain, has been obtained.