The effects of various tetrasubstituted ammonium compounds on the solubility of deoxygenated sickle hemoglobin were evaluated. These conclusions were drawn from the slopes of the solubility profiles obtained: (1) for the homologous series of tetraalkylammonium chloride salts (R4NCl), antigelling potency increased with increasing chain length of the R group: Ch3 less than C2H5 less than C3H7 less than C4H9; (2) for halide salts of the tetrabutylammonium cation there was no difference in effectiveness among the anions examined (Br-, Cl-, F-), presumably because of the extremely potent salting-in effect of this cation; (3) substitution of a benzyl for an alkyl group in three tetraalkylammonium chloride salts, C6H5CH2(R)3NCl, where R = CH3, C2H5, or C4H9, potentiated the antigelling capacity by as much as eight-fold. Because they are substantially more water soluble than any other class of noncovalent inhibitors examined to date, further manipulation of the aryl substituent on these compounds may contribute to the design of an effective antisickling agent.