The use of algae for therapeutic purposes has a long history (Glombitza and Koch 1989), and the systematic examination of algae for biologically active substances, especially antibiotics began in the 1950s. Early studies were concerned mainly with in vitro studies of the action of the compounds and it was only in the 1970s, at the Roche Research Institute of Marine Pharmacology (RRIMP) in  Australia, that the focus shifted to emphasize in vivo examination of activities using a very extensive range of screens (Baker 1984; Reichelt and Borowitzka 1984). RRIMP also pioneered the screening of crude extracts rather than pure compounds, and the use of bioactivity in the screens to direct the isolation and identication of the active compound (Baker 1984). This approach is now the most commonly used and is illustrated in Figure 14.1.