A weakly positive IgM for Mycoplasma pneumoniae is indicative of mycoplasma infection and suggests that it is in the early stages of infection. Mycoplasma antibodies are divided into IgM and IgG antibodies. IgM antibodies are produced relatively early, and may appear about a week after infection with mycoplasma, and the antibody titer is highest at 3-4 weeks, after which the antibodies gradually decline and are accompanied by positive IgG antibodies. Therefore, there are two cases of positivity, one at the early stage of infection; the other case is that IgM antibodies are about to disappear and IgG antibodies have been produced. In either case, it means that the body has been infected with mycoplasma.