A flow injection system for cobalt determination in faeces of bovines and equines receiving Co-EDTA as a tracer in animal nutrition studies is proposed, using 1.0 mol HCl l(-1) as extracting medium, and detection by flow injection spectrophotometric procedure based on the catalytic effect of Co(II) on the oxidation of Tiron by hydrogen peroxide. Linearity was observed up to 8.0 mu g Co l(-1), and the detection limit was 0.2 mu g Co l(-1) (3 s blank). The system requires 0.12 mg Tiron per determination and handles 65 samples h(-1). No baseline drift was observed during extended operation periods (8 h) and precise results (r.s.d.<l%) were detected. Accuracy was confirmed by running several faeces samples already analysed by flame atomic absorption spectrometry. Results related to the HCl extraction procedure were in close agreement with those obtained using the nitric-perchloric digestion (y=0.978x+0.101, R-2=0.9848), suggesting that HCl extraction and flow injection determination can be used routinely for rapid analysis of cobalt in faeces, (C) 1998 Elsevier Science B.V.7417984