Female rabbits (n = 36, 6 per group) were immunized with: (i) solubilized isolated porcine zona pellucida (SIZP), which contains ZP1, 82 kDa; ZP3 alpha, 55 kDa; and ZP3 beta, 55 kDa; (ii) a purified preparation of ZP3 alpha and ZP3 beta (ZP3); (iii) purified endo-beta-galactosidase digested glycoproteins ZP3 alpha-(EBGD) and (iv) ZP3 beta-(EBGD) (each about 30% deglycosylated); (v) chemically deglycosylated core proteins ZP3 alpha-(DG) and (vi) ZP3 beta-DG (each greater than 92% deglycosylated). Rabbits injected with saline (n = 6) or Freund's adjuvant (n = 6) served as controls. Rabbits were bled weekly to monitor titres. Every six weeks two animals from each group (n = 16) were selected for unilateral oophorectomy followed by histological examination. Sections were scored for numbers of primary, secondary and tertiary follicles. Anti-ZP3 titres developed in all treatment groups and correlated with carbohydrate content (peak per cent [125I]-labelled ZP3 binding by radioimmunoassay: SIZP 71.9 +/- 1.2, ZP3 70.0 +/- 2.5, ZP3 alpha-EBGD 60.9 +/- 5.3, ZP3 beta-EBGD 56.4 +/- 5.0, ZP3 alpha-DG 56.4 +/- 4.0, ZP3 beta-DG 53.5 +/- 4.3) (means +/- SEM). Animals immunized with SIZP, ZP3 and ZP3 beta-EBGD showed a statistically significant reduction in the number of primary, secondary and tertiary follicles compared with controls (P less than 0.01, MANOVA), whereas animals immunized with ZP3 alpha-EBGD, ZP3 alpha-DG and ZP3 beta-DG did not (P greater than 0.05, MANOVA). These results demonstrate that immunization with purified ZP3 alpha macromolecules (ZP3 alpha-EBGD, ZP3 alpha-DG) or ZP3 beta-DG does not produce histopathological changes in ovaries. Such deglycosylated ZP macromolecules represent potential target antigens for immunocontraceptive development.