A series of chiral spirocyclic cyclodipeptides of the general formula I was synthesized; the aim was to determine how the substitution of cyclobutane for cyclopentane in cyclo(-alanyl-1-amino-1-cyclopentanecarbonyl-) would influence the inhibition of the proliferative activity of the caudal morphogenic system (CMS) of Chick embryos. Spirocyclic cyclodipeptides Ia - Il were obtained by cyclization of linear dipeptides IIa - IIf, prepared by condensation of protected amino acids by DCCI method. The inhibition was investigated by the Chick Embryotoxicity Screening Test. The results show generally lower activity in the tested series, as compared with derivatives containing 1-amino-1-cyclopentanecarboxylic acid.