Bovine viral diarrhoea continues to be an important disease affecting both beef and dairy animals of all ages. One of the quickest means of measuring bovine viral diarrhoea virus (BVDV) exposure and infection in the herd is a serum neutralization (SN) assay. Type 1 and type 2 BVDV SN results from the Animal Disease Research and Diagnostic Laboratory at South Dakota State University were collected over a seven-year period (1995-2001) to determine any trends. These results indicated that in 1996, 31% of the animals had titres > or =512 while in 2001, 74% of the titres were > or = 512. There has been a progressive increase over the seven-year period in the number of cases with titres > or = 512 with the exception of 1999 when there was a slight decrease. When analyzing the titres greater than 512, a further increase was seen. In 1995, 80% of the titres were < or = 1024 and 20% were 2048 and no titres were >2048. In 2001, 47% of the antibody levels were < or = 1024 while 53% were < or =2048 and 30% were >4096. The most dramatic increase in titres occurred in 1997 and the percentage of animals with titres from 512-8192 has remained fairly constant for the last five years (1997-2001). This increase is in part due to more extensive use of vaccination but probably also reflects a rise in field infections. In the future, standardizing existing BVDV SN serology along with developing new BVDV serology methods is necessary to provide continuity for any full-scale eradication programme.