The flow of chromatin from the nuclei of mouse liver cells and spermatozoa after treatment with concentrated saline and detergent solutions under the simultaneous action of gravity results in the formation of extended chromatin fibers (ECF). In mouse somatic nuclei, the increase in chromatin condensation is accompanied by a decrease in the frequency of ECF formation. Since tightly packed chromatin with a very lysine-rich histone variant that resembles somatic H1 histones occurs in honey bee spermatozoa, we examined the formation of ECF in sperm cells of Apis mellifera, and compared the findings with data for mouse cells. Freshly prepared smears of fixed and unfixed semen from A. mellifera were lysed under the action of gravity, stained with toluidine blue at pH 4.0, and examined with polarized and unpolarized light. A protocol using unfixed preparations and a short lysis period that resulted in abundant ECF production in mouse hepatocytes (which contain loosely-packed chromatin) and sperm cells produced ECF in only a few spermatozoa of A. mellifera. In contrast, a protocol using fixed preparations and a long lysis period produced fewer ECFs in the former two cell types and no ECF formation in honey bee spermatozoa. The limited chromatin fluidity in A. mellifera spermatozoa may reflect their special DNA-protein composition and organization in the cell nuclei, the participation of nuclear matrix elements, a less effective disruption of the nuclear envelope and plasmalemmal components during lysis, and/or cytoplasmic spatial constraints resulting from particularities in the acrosomal complex.