Various 1'-(o, m, and/or p-substituted benzyl) (5), 1'-(heterocyclic arylmethyl) (6), and 1'-acyl (7) analogs of spiro [isochroman-3, 4'-piperidin]-1-one were prepared and tested for inhibitory activity on the compound 48/80-induced release of histamine from mast cells. The biological results suggested that the activity is mainly affected by the lipophilicity rather than by the electrostatic character of the 1'-substituent. 4-Benzylspiro [cyclohexane-1, 3'-hexahydroisochroman]-1'-one (17) and 9-benzyl-1-oxaspiro [5.5] undecan-2-one (18) were prepared and found to be inactive, implying that the benzene moiety in the isochroman ring is essential for the activity.