Over nearly the last 30 years the standard investigation method for identification of monoclonal immunoglo- bulins (paraproteins) was based upon electrophoresis of serum proteins and in case of a positive M-gradient on subsequent immunoelectrophoresis. Now, electrophoretic systems of a high quality, which for example, use agarose as a dividing medium, are able to identify small M-gradients in concentrations of about 1 g/l. Immuno- electrophoresis has been practically fully replaced by immunofixation. The high sensitivity of immunofixation leads not only to identification of small paraproteins but also oligoclonal gradients. We are from time to time faced with the dilemma, of whether the gradient should be evaluated as monoclonal or oligoclonal. In a series of 2 413 paraproteins analyzed by immunoelectrophoresis doubled paraproteinaemias were found 42 times, i.e. a frequency of 1.7%. In the last two years we found 202 paraproteins by means of immunofixation electrophoresis and within this group multiple paraproteinaemias were found 21 times, i.e. a frequency of 10.4%. Immunofixation reveals that multiple paraproteinaemias are more frequent than was assumed.

        Key words: monoclonal immunoglobulin, electrophoresis, immunofixation, multiple paraproteinaemias.