The objective of this study was to establish a range of reference values for blood gas analysis, electrolytes, hematocrit and critical blood variables for guinea pigs anaesthetized with xylazine-ketamine. The influence of the strain (short hair English vs. Duncan-Hartley) was also evaluated. Blood was obtained by cardiocentesis from 40 clinically healthy 8-11 weeks old female adult guinea pigs. Results indicated the following values: pH (7.28-7.55 vs. 7.38-7.53), PCO2 (28-42 vs. 33-44 mmHg), PO2 (18-70 vs. 25-52 mmHg), Na+ (124-141 vs. 126-137mmolL-1)K+(3-7.5 vs. 3.6-4.6mmolL-1),Ca2+(0.52-1.28 vs. 1.28-1.47 mmolL-1),glucose (64-190 vs. 98-211 mg dL-1), lactate (1-5 vs. 0.3-6.6 mg dL-1) and hematocrit (27-40 vs. 38-49%) for short hair English and Duncan-Hartley guinea pigs, respectively. No differences in the guinea pigs electrolytes or blood gas analysis were found. However, we can confirm that the individual's pigmented short hair English strain showed the most favorable results in regard to the PCO2, Ca2+ and haematocrit values when submitted to the sedation combination of xylazine-ketamine.