Abstract: The potentials of heterologous red blood cells (RB) indicator systems for differential assay of vaccinal and field (natural) ND antibodies were investigated. In a preliminary experiment on the Haemagglutination (HA) and Haemagglutination Inhibition (HI) standardization tests, results showed that 0.5 and 1% of goat and guinea-pig red blood cells (RBC) suspensions gave similar results with tests conducted with standard or control 0.5% chicken RBC as indicator systems. The HA time for the standardized tests were 50 and 52 minutes with the goat and guinea-pig RBC indicator systems while the corresponding Elution times (Elt) were 86 and 120 minutes respectively. In a field trial using the heterologous indicator systems on the HI test of sera obtained from conventional (field ) poultry flocks with or without history of ND, the HI titres with the guinea-pig indicator systems was selectively and consistently higher than titres with the standard chicken RBC by 5log2 in flocks with confirmed ND history. However, the titres for flocks without ND outbreak were generally similar with the three indicators thus showing the ability of the guinea-pig RBC indicator for the selective detection of high titre in ND infected flocks. The ability of these indicators as tools for differential detection of vaccinal ND antibodies in routinely vaccinated chickens was also investigated. The results showed that the ND vaccinal antibodies detected by the three indicators were similar or identical and ranged from 2log2 in one group to 9log2 in another. This strengthened the findings that the selective ability of the guinea pig RBC was only on antibodies due to ND natural outbreaks thus fulfilling the demand for a serological test that could differentiate between vaccinal and natural ND outbreak (field) induced antibodies.