Bagdasarian et al. (1964) have discussed the difficulties in separating compounds of low molecular weight from proteins, and the advantages of using a volatile solvent, such as phenol~acetic acid~water (1 : 1 : 1, w/v/v) (referred to as solvent A in the remainder of this paper), to achieve this separation. Trichloroacetic acid is also efficient in effecting this separation (Bagdasarian et al. 1964), but it dissolves glycoproteins (Bell 1963; Stenzel et al. 1964 ; Jennings and Watt 1967) and some of the wheat flour proteins (Bell 1963) and is difficult to remove from solutions.