The purpose of this study was to determine the value of conventional and newer serological tests (toxoplasmic serological profile) in the diagnosis of toxoplasmic lymphadenitis (TL). We studied 40 consecutive patients with biopsy-proven TL. Cervical, axillary, or occipital adenopathy was present in 72.5%, 20%, and 7.5% of the patients, respectively. Low-grade fever, fatigue, general malaise, or sore throat were present in only 6 (15%) of the 40 patients. A positive result for all serological tests was time dependent from the clinical onset of lymphadenopathy. The initial serum samples were positive for antibody for each patient, as shown by a Sabin-Feldman dye test. Between 3 and 6 months after clinical onset of TL, all of the patients had antibody titers of > or = 1:1,024. The ELISA was positive for IgM antibodies in all of the patients in the first 3 months. Detection of IgA or IgE antibodies or an acute pattern in the differential agglutination test was helpful in diagnosing TL in those patients who had negative, low-positive, or equivocal titers of IgM antibodies (as measured by ELISA) after 3 months. A toxoplasmic serological profile on the first serum specimen drawn after clinical onset of TL had a sensitivity of 100%. It is advisable to obtain such a serological profile in cases of asymptomatic lymphadenopathy before biopsy is carried out, especially for those individuals who have negative or equivocal IgM antibody titers.