Monthly serological follow-up of the antibody titres against Leishmania infantum in hunting dogs in rural southern Spain was carried out during the transmission period (from April to October in 1996). Titres > or = 160 were regarded as indicating disease, while lower positive tires were also recorded as 'seropositive'. Over this period, a significant (p < 0.05) increase in the percentage of dogs with a titre > or = 160 was observed; from 12.6% in April to 19.2% in October. The same pattern was observed with the seropositives (titre > or = 20) which increased from 36.3% in April to 55.6% in October. Of seronegatives in April, 60% were still negative in October whereas 22% had a titre of 20-40 and 18% had a titre > or = 80. Similarly, 68% of those with a titre > or = 80 in April still had a titre in this range in October, 25% of the titre had decreased to 20-40 and in 7% to a zero titre. The most noteworthy is that 25% of animals reached titres of > or = 80 and decreased to zero or 20 more than once. Parallel to this study, another survey was conducted on dogs from Granada city centre. The seroprevalences (titres > or = 160) at the start and the end of the transmission period were 1.7 and 3.7% respectively and the seropositively values were 12 and 11% respectively.