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The efficiency of indirect immunofluorescence for detection of respiratory syncytial (RS) virus antigens in nasopharyngeal secretions was compared with virus isolation on highly sensitive cell culture systems maintained in serum-free media. Twenty out of 22 (91%) culture-positive specimens were correctly identified by indirect immunofluorescence, which gave no false positive results. Since clinical specimens were sometimes unsuitable for immunofluorescence studies, this could explain two false negative results. Thus, this technique proved to be a reliable tool for early diagnosis of RS virus infections; however, in order to avoid false negative results, it should be combined with sensitive cell culture isolation systems.

A simple rapid technique for detection of mycoplasma contamination in cell cultures by a modified Hoechst 33258 staining procedure, is described. After brief alcoholic fixation in situ, cell monolayers were definitively fixed and simultaneously stained by the addition of a 0.001% (w/v) Hoechst 33258 fluorochrome solution in ethanol for a few minutes. This method and conventional mycoplasma isolation techniques resulted in comparable sensitivity. Mycoplasma contaminants were detected in 21 out of 217 cell culture specimens tested. However, two different specimens were positive only by either procedure. A sequential use of both techniques, based on the search for mycoplasma contamination by microbiological methods only in Hoechst 33258 - negative samples, should provide a reasonable degree of sensitivity, being also accessible to virtually every laboratory involved in tissue cuture work.