SummaryMethods of production and characterization of immune typing reagents reactive with the erythrocytes of the dog are described. Five of the reagents (agglutinins) were reactive with previously unknown blood group factors and were shown by statistical and genetic tests on 222 random samples and 28 families to belong to 5 previously unrecognized blood group systems. The five new systems were one‐blood factor, two‐allele, three‐genotype systems like the B, C, D and F systems. These were arbitrarily named J, K, L, M