What field studies need to be carried out in order to test the hydrotherrnal model for the origin of life? This question was already raised in 1989 by the workshop in Prague on 'Chemical Evolution and Neo-Abiogenesis in Marine Hydrothermal Systems' (Holm, 1990). The full range and diversity of hydrothermal environments can only be revealed if more exploration work is carried out on a world-wide basis. Much progress has been made in understanding the controls on the hydrothermal fluids of individual areas, but extension to a global context remains difficult (cf. Von Datum, 1990). In Chapter 2 off-axis hydrothermal systems are discussed, pointing out that only minor surveys have been directed towards this type of hydrothermal activity, even though the amount of water which circulates through off-axis systems is estimated to exceed that of on-axis systems by a factor of between 20 and 25.