The concentrations of C‐reactive protein (CRP) in serum from dogs diagnosed as normal by clinical, haematological, and biochemical examination were determined by enzyme‐linked immunosorbent assay (ELISA) and slide reversed passive latex agglutination (RPLA), using IgG antibody isolated from rabbit anti‐canine CRP serum. The mean value of CRP in 66 normal dogs kept in private households was 8.4± 4.9 μg/ml by ELISA and 8.5± 6.3 μg/ml by RPLA. Thus, no significant difference was demonstrated between the values obtained by ELISA and RPLA. No significant age and sex‐related differences were found in the CRP values. The mean concentration of CRP in 84 6‐month‐old Beagle dogs kept in kennels by breeders was 6.2±3.9 μg/ml by ELISA and 8.0±4.0 μg/ml by RPLA. Again no significant difference was found. The CRP values determined by ELISA and RPLA were closely correlated (r=0.913). The serum and plasma concentrations of CRP measured by RPLA were also closely correlated (r=0.994). This indicates that plasma can be used as well as serum to determine CRP concentrations by RPLA.