A discrimination study of the neurotransmitters 3,4-dihydroxy-L-phenylalanine (DOPA), adrenaline, noradrenaline, tyramine and serotonin in aqueous solution utilising hydrophobic and hydrophilic yoctowells bearing oligoethylene walls is reported. The catecholamines were bound selectively to the hydrophobic yoctowells. Serotonin showed a preference for hydrophilic yoctowells. [image omitted].