A geographic information system (GIS) is being developed to study the spread of pseudorabies virus (PRV) among swine herds in the state of Minnesota. This GIS features an interface with a database management system that stores and manages pertinent data. These data include herd size, type of production system, degree of confinement, topographical features surrounding the farm, density of swine herds and distance to the closest quarantined herd. A pilot study was conducted in one Minnesota county with 280 swine herds, of which the PRV status was known in 115. Cox regression analysis was used to determine factors associated with herd PRV status. Relative risks (RR) and 95% confidence intervals (CI) were calculated. No association was detected between the PRV status of the herd and distance to the nearest county road, highway or quarantined herd. However, the following factors were significant: located within 1 km of a river or lake (RR, 0.524; CI, 0.328-0.828); farrow to finish (RR, 2.120; CI, 1.194-3.791); complete confinement (RR, 3.423; CI, 1.639-7.139); density of swine herds within a 5 km radius (RR, 1.036 per herd; CI, 0.996-1.064).