Aim The aim is to determine the importance of the anti-measles Ig M determination in the differential diagnosis of this disease with other diseases accompanied by rash during the modern course of measles in children, that is, its role in determining whether the rash is caused by measles.

Material and Method 50 children suspected of having measles due to their rashes aged 1–17 years old were clinically and laboratory examined. Anti-measles Ig M was determined in these children on the 7–10th day and the 12–16th day of the desease.

Results Based on the results, the patients were divided into 2 groups. In 14 children(28%) with rash and fever included in the first group, on the 7–10th day of the disease a slight increase in anti-measles IgM was found, and on the 12–16th day of the disease when the symptoms of the disease passed, anti-measles Ig M decreased and completely normalized. The fact that IgM did not increase in dynamics, but on the contrary normalized, showed that the rash was of non-measles origin. In 36(72%) children included in group II, on the 7–10th days of the disease the anti-measles Ig M increased and became positive, and in dynamic, on the 2nd week of the disease increased, reached its peak, thus confirming the origin of the rashes in these patients.

Conclusions Conclusion As it can be seen, in several other diseases accompanied by rash, anti-measles Ig M can be false positive on the 7–10th day of the disease, that is, a slight increase of this indicator during this period does not prove the presence of measles. Anti-measles Ig M test in the 2nd week of the disease is important and informative to make sure that the disease is measles based on the rash.