Twenty nine West African Dwarf goats were randomly allotted to either a diet of pelleted lucerne with a high N content (Crude protein level=172 g/kg DM; n=14) or chopped grass straw with a low N content (Crude protein level=68 g/kg DM; n=15). Nine animals fed lucerne and 10 animals fed grass straw were infected with Trypanosoma vivax to study its effects on feed intake and efficiency of N utilization during the first 6 weeks of infection. Infection reduced organic matter intake (OMI) from 55 (s.e. 2) to 38 (s.e. 2) g kg-0.75 d-1 (P<0.001). OMI was not affected by feed type (P>0.10). The relative decrease of digestible organic matter intake (DOMI) due to infection was the same in animals fed lucerne or grass straw (36 and 35%). Retention of N was lower in infected animals and in animals fed grass straw. By relating N retention to DOMI the efficiency of N utilization, corrected for feed intake level, was estimated. No effect of infection or feed type on the efficiency of N utilization was detected. One overall regression equation was estimated: N Retention=-0.45 (s.e. 0.04) 0.017 (s.e. 0.002)xDOMI (n=29; r2=0.86). Serum urea concentration was higher in the goats fed lucerne than in the goats fed grass straw; only in the lucerne group, infected animals showed a lower serum urea concentration post infectio (p.i.) than control animals. Serum creatinine concentration was higher in grass straw-fed animals than in lucerne-fed animals. From the former group, infected animals had a lower creatinine concentration p.i. than controls. It is concluded that infection affected feed intake, but not the efficiency of N utilization.