Blood characteristics in dielectric, haematological and biochemical terms of the fish Cyprinus carpio exposed to a sublethal concentration of sodium alkyl benzene sulphonate were compared with those from untreated control fish; recovery from the test solution was also checked. Trends of change in the majority of chosen parameters of blood with time of fish exposure to anionic detergent were significantly linear. A decline was noted in erythrocyte count, haematocrit, blood haemoglobin concentration, mean corpuscular haemoglobin concentration and mean corpuscular haemoglobin with the exception of mean cellular volume. An uptake of sodium into red blood cells and a rise of intracellular potassium were seen. Practical indicators of the presence of detergent in fish blood were obtained from dielectric beta dispersion measurements. It has been shown that dielectric parameters could be correlated with haematological parameters but not with biochemical ones. Results indicate that changes in haematocrit induce a corresponding variation of the maximum of the dielectric loss factor tan delta An increase in the electrical conductivity and permittivity of the erythrocytes' interior in exposed fish was associated with a decline of mean corpuscular haemoglobin.