[Instability of the DNA content in Entamoeba histolytica]

DNA content was repeatedly determined during a 10-month period on axenically cultured tropho-zoites from three strains (HK-9:NIH, HM-2:IMSS and HM-3:IMSS) and a clone of HK-9:NIH strain of Entamoeba histolytica, by means of the diphenylamine reaction. Average DNA content was more or less variable in all of them. According to their extent, variations were: 1) large (almost four times in strain HM-2:IMSS), or 2) small (1.5 times in the clonal isolate). With this relatively small sample, three statistically different groups were formed with nuclear DNA averages (1.35, 2.05 and 7.78 picograms respectively). Changes of ploidy and/or genomic heterogeneity in trophozoites could be the main causes of the striking instability in their DNA content.