Twenty-two 2-week-old Japanese quails (Coturnix japonica) with retained yolk sac have been assessed using validated standard procedures to quantify the serum concentration of the acute phase reactants (haptoglobin and serum amyloid A), inflammatory mediators (tumor necrosis factor-alpha, gamma interferon) and gangliosides (total sialic acid, lipid bound sialic acid and protein bound sialic acid). The present findings show that the concentrations of all measured parameters in diseased birds were significantly higher than the control group. Inflammation following yolk sac infection/retention leads to stimulation of the synthesis of inflammatory mediators, acute phase reactants and gangliosides. Among the study variables, lipid bound sialic acid had the most obvious change, so it is the most sensitive parameter.