Oligosphere Medium (OsM) is a complete medium designed for optimal growth of normal human oligospheres in vitro. It is a sterile, liquid medium which contains essential and non-essential amino acids, vitamins, organic and inorganic compounds, hormones, growth factors, trace minerals and factors prevent oligospheres attachment during culture. The medium is serum-free. It is bicarbonate buffered and has a pH of 7.4 when equilibrated in an incubator with an atmosphere of 5% CO2/95% air. The medium is formulated (quantitatively and qualitatively) to provide a defined and optimally balanced nutritional environment that selectively promotes growth of normal human and animal oligospheres in vitro.