Levitus (1982) climatology has been used to identify four extrema, three maxima and one minimum, in the vertical salinity profiles in the Arabian Sea. Their geographical distribution, depths, theta-S characteristics, and seasonal variability are described. Two of the maxima arise from the influence of Red Sea and the Persian Gulf Water. The third, which lies at the bottom of the Equatorial Surface Water, forms due to freshening at the surface of high salinity Arabian Sea near-surface waters. The dominant factors leading to the dormation of the little known subsurface salinity minimum appear to be, (1) transport of the low salinity water by the northeast monsoon coastal current along the west coast of India and subsequent increase in the surface salinity of this water due to evaporation in the North Arabian Sea, (2) poleward coastal undercurrent along the west coast of India during the southwest monsoon. The theta-S characteristics of the four salinity extrema are used to put into perspective the structure of the Arabian Sea water masses