IgE antibodies to Mycoplasma pneumoniae antigens were measured by RAST assay in 152 patients with asthma and other IgE and non-IgE mediated diseases. Five patients with asthma and/or atopic dermatitis had highly elevated Mycoplasma RAST binding ratios, p < 0.001. For these five patients the ratios ranged from 1.78 to 4.74. These increased ratios persisted at least two to 16 months in three of four individuals who were evaluated sequentially. RAST inhibition studies using Mycoplasma pneumoniae, Mycoplasma control, Streptococcus MG and viral antigens showed the specificity of binding for M. pneumoniae in these five patients indicating the presence of IgE antibodies to M. pneumoniae.