Abstract: A ready-for-use rapid test package for carrying out serological investigations in which at least two of the following reactants:(1) patients serum;(2) erythrocytes;(3) amboceptors specific for the erythrocytes;(4) complement and(5) a reactant selected from the group consisting of antigen and antibodies not belonging to reactant class (3)Are reacted with each other, the package containing at least two of the reactants in a solid and preserved form, in quantities suitably adjusted to each other, to carry out the test.The package provides the clinician or serological laboratory with reliable and simple means of carrying out the complement binding reaction without the complicated adjustments of the activities of the different reactants.