Background: Serum free light chain analysis is now well established in the investigation of monoclonal gammopathies. In the UK there has, until recently, been a single supplier of kits for such analysis. Recently, a second method using monoclonal antisera was introduced. We have compared the performance of these two kits in four routine laboratories. Method: Samples submitted for routine analysis (327 samples, 258 [79%] from patients with B-cell lymphoproliferative disease) for serum free light chains were tested by both technologies (Freelite, Binding Site and N Latex FLC, Siemens), according to the manufacturers' instructions. Results: Qualitative data were available by both methods on 313 samples for serum free kappa chains and 324 samples for lambda free light chains. We found poor correspondence of 81% for kappa and 74% for lambda. Five percent of samples were significantly discordant in these assays. Conclusions: These assays perform very differently in clinical practice. They cannot be used interchangeably, especially if monitoring patient responses to therapy.

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In a random sample of eera from a predominantly male group of hoepital patients with an average age of 67, complementdixing antibodies were found in 20 per cent to M. horninis type 1, in 16 per cent to Unknown Strain CE 5, in 1 per cent to M. pharyngis and in 2 per cent to M. pneumoniae.These percentages are lower than thoee reported in the literature for younger populations of patients. Thus the immunological experience with mycoplasmas ( pleuropneumonia-like organisms) varies from one population to another. In general, however, the incidence of mycoplaemal infection eeeme to be lower in older than in younger populatione.The findings also indicate that the mere isolation of these organisms from the sera of patients who manifest a dieease process doee not constitute evidence of an etiological relation. rhip unlees other correlates can be established.Until recently the study of mycoplasmas (PPLO or pleuropneulnonia-like organisms) has been one of the neglected areas of microbiology (I). Since 1962, however, when Chanock and associates (2) isolated and characterized a my coplasma from patients with atypical pneumonia, the importance of these organisms in human disease has been recognized. In 1965 Mufson et al. (3) demonstrated that exudative pharyngitis could be produced in volunteers experimentally infected with Mycoplasma horninis type 1. Several studies have indicated the possibility that mycoplasmas may be involved in other diseases. Fahlberg et al. (4) isolated mycoplasmas from the synovial fluid in 22 of 24 patients with rheumatoid arthritis, and Bartholomew (6) isolated these forms from 14 of 17 patients with rheumatoid arthritis, systemic lupus erythematosus or Reiter's syndrome.Clark and associates (6) established that antibodies to mycoplasmas in human serum can be detected readily by complement fixation, and such studies have been conducted on populations of young patients in whom infection with