Three hundred and forty three chicks in total, belonging to two lines, R' and R-, respectively bred for a high and a low « residual component of feed intakc at the adult stage, were distributed in a control group and a group inoculated at the age 25 days with 10 6 oocysts of Eimeria acervulina (duodenal coccidiosis). The birds were slaughtered seven days after the inoculation. The body weight variation, the feed intake during the experimental period, oocyst excretion, lesion score and other clinical signs, together with several blood parameters (glucose, proteins, enzymes, corticosterone) were measured. In addition to the depression of growth rate, feed intake and feed efficiency and the appearance of characteristic lesions, the effect of the inoculation by E. acervulina on the recorded blood parameters are briefly discussed. A complex interaction between sex and treatment is noted for glucose and alkaline phosphatase. On the contrary, for body weight gain and lesions, no such interaction is observed. For their response to treatment, the two lines differ neither for body weight variation, nor for feed consumption ; the distribution of the lesion score suggests a slightly higher mean value in the R-line. In this line, on the other hand, the ot2-globulins increase more in response to the treatment than in the R + line. Independently of the response to the pathogen, the lines differ in the level of total proteins in the serum (higher in R + by about 10 % in both treatments), in the level of corticosterone (higher in R + , mainly in the control). The glucose on the whole has a higher value and the esterase has a noticeably lower value in the R-line, but with interactions with sex and treatment. The caeruloplasmin level shows a line x treatment interaction and alkaline phosphatase shows a line x sex interaction.