The aim of the study was to investigate the effects of poultry red mite (PRM) infestation on Japanese quail. Two trials were carried out under same conditions, each using 80 one-week-old quail chicks. Half of the chicks were experimentally infested with PRM and the other half functioned as control group. The conditions of the two trial rooms were the same. Low infestation was observed in Trial I, while high infestation was seen in Trial II. Live weight (LW) and daily feed intake (DFI) were not significantly affected in Trial I (P = 0.2190). However, infested birds scratched themselves 2.46 times more than the control birds (P = 0.0002). Haemoglobin (Hg) of control and infested birds were 9.58 g.dl(-1) and 7.72 g.dl(-1) (P = 0.0017), and eosinophil proportions 5.79% and 18.58% (P = 0.0004), respectively. In Trial II differences of LW between control and infested birds reached a significant level at the 5th week (P = 0.0038). DFI of control birds was higher than in infested birds (P < 0.0001). Infested birds showed 4.22 times more scratching behaviour than the control (P = 0.0003). Hg, erythrocyte and haematocrit were 5.52 g.dl(-1), 1.79.10(6).mu l(-1) and 29.36% in infested birds, respectively; 11.28 g.dl(-1), 3.78.10(6).mu l(-1) and 43.47% in the control (P = 0.0001). Ratio of the spleen to carcass weight was 0.08% in control and 0.10% in infested birds (P = 0.0595). The ratio of gizzard to carcass weight was higher in infested birds (P = 0.0008). A higher mortality in infested birds was observed in Trial II compared to Trial I (P < 0.0001). The carcasses of infested birds showed lower dry matter content than carcasses of control birds (P = 0.0006). In conclusion, a low level of infestation did not lead to major negative effects, but decreased haemoglobin levels and increased scratching behaviour of the infested birds, indicating a negative impact on welfare. However, high infestations of PRM had severe effects on the quail.