Campath 1-H (Alemtuzumab) is a humanised monoclonal antibody which targets the CD52 antigen, a low molecular weight glycoprotein present on the surface of most lymphocyte lineages, causing complement mediated lysis and rapid and prolonged T lymphocyte depletion. Following encouraging initial data from other centres we report our open label experience of using Campath 1-H as a treatment in aggressive relapsing multiple sclerosis in a consecutive series of 39 highly selected patients treated across three regional centres and followed for a mean of 1.89 years.