A 10 year old boy presented to the outpatient clinic at the end of the summer. Five days earlier he had developed fever of up to 38 °C, associated with malaise, fatigue, headache, left-sided, ear ache, sore throat, rhinorrhea and cough. He was not on medication and his past medical history was unremarkable. Physical examination revealed pharyngitis and bilateral otitis media. The liver, spleen and lymph nodes were not palpable. The X-ray chest was normal and Mantoux test was negative. The laboratory findings were as follows: Ht 44%, Hb 13,6 g/dL, WBC 1.3x10⁹/L (neutrophils 65%, lymphocytes 33%, monocytes 2%, eosinophils 1%, see fig.1), platelets 178x10⁹/L, SGOT 25 IU/L, SGPT 30 IU/L, γGT 25 IU/L, serum billirubin 0.8 mg/dL, LDH 210 IU/L, CRP 5 mg/dL, ESR 50 mm/1 hour. Serological tests showed high agglutinin titers and later high titers of antibodies against Mycoplasma pneumoniae. The diagnosis of mycoplasma infection was established, and he was treated with clarithromycin 15 mg/kg/day, divided into two doses, for ten days. At 2-week follow-up all the symptoms and clinical findings had disappeared. His new blood count showed: Ht 43.8%, Hb 13.4 g/dL, WBC 7.4x10⁹/L, with normal differential count. The blood smear was similar to that at presentation and as there were no other symptoms or signs to explain the finding on his blood smear, we requested a blood count and smear from his mother, the findings of which (fig.2) established the diagnosis.