In 1987 we conducted a sero-epidemiological survey in the Murcia Region (South-East Spain) to discover the prevalence and spread of PRCV-infection among breeding pigs and farms and determine the association between herd size and geographical zone with PRCV-infection. The Murcia Region was divided into four geographical zones and the farms classified by size in four categories. The random sample was statistically representative of both the breeding stock and farms in each geographical zone. We analysed 6,000 breeding pigs from 480 farms. The immunological techniques employed were indirect ELISA and blocking ELISA. The prevalence (P +/- IC) of PRCV-seropositive breeding pigs and infected breeding farms was 14.53 +/- 0.89% and 21.87 +/- 7.83% respectively. On 55% of the infected farms, the prevalence of seropositive breeding pigs was 60-100%. PRCV-infection appears spread throughout the four geographical zones of the Murcia Region. However, a significant association (p less than 0.01) was observed between geographical zone and the prevalence of PRCV-infection. A herd size of greater than 50 breeding pigs had a greater risk (p less than 0.01) of PRCV-infection.