Current literature suggests that severe anemia in dogs and cats increases plasma lactate (PL) levels. The aim of this prospective pilot study was to test the hypothesis that PL levels are increased in clinical patients (dogs and cats) presented with symptoms of anemia. Furthermore the correlations between PL, PCV and clinical symptoms were studied. 20 dogs and cats with a history of anemia (PCV < 0.2 l/l) were included. To exclude hypovolemia and dehydration as a potential reason for hyperlactatemia all patients were rehydrated intravenously with a nonlactate electrolyte solution Following rehydration pulse rate, respiration rate, body temperature, PCV, total solids and PL were recorded. 13 dogs aged from 3-14 years (M: 8 years), weight from 2.5-32 kg (M: 25 kg) and 7 cats aged from 1.5-13 years (M: 6 years), weight 3.4-7 kg (M: 5 kg) were included in the study The duration of the clinical symptoms of anemia was 1-7 days (M: 4 days) in dogs and 1-35 days (M: 4 days) in cats. After rehydration laboratory parameters were: PCV 0.07-0.20 l/l (M: 0.16 l/l), TS 44-66 g/l (M: 56 g/l), PL 1.3-4.74 mmol/l (M: 2.83 mmol/l) in dogs and PCV 0.08-0.18 l/l (M: 0.14 l/l), TS 46-84 g/l (M 6.4 g/l) and PL 1.28-6.42 mmol/l (M: 1.93 mmol/l) in cats. PL was elevated in 3 cats (43 %) and 7 dogs (54 %). The correlation coefficient (r) of PL with heart rate and respiration rate was -0.006 and 0.102 in dogs and 0.376 and 0.663 in cats. PCV correlated with PL in dogs (r = -0.217) and in cats (r = 0.475). Thus, half of the dogs and cats had increased PL levels which did not correlate with PCV level. An increase in respiration rate is the most common clinical sign in animals with anemia and increased lactate. The results suggest an insufficient oxygen supply to the tissue, which should be remedied by oxygen application.