Streptococcus agalactiae responds very well to intramammary antibiotic treatment. This allows a system of ‘blitz therapy’ to be used to eliminate these infections. Blitz therapy involves antibiotic intramammary treatment into all four quarters during lactation to eradicate S agalactiae infections. Its use became popular in herds with high cell counts that were caused by S agalactiae. Cell counts have fallen significantly since the early 1980s, and the prevalence of S agalactiae and the need to employ blitz therapy has reduced. This article discusses the epidemiology, diagnosis and therapeutic options where S agalactiae is the sole or predominant cause of a high cell count. It describes how to decide whether blitz therapy is appropriate, outlines the key principles of treatment and highlights how to avoid any subsequent problems.