While standard techniques for obtaining megabase-size DNA from microorganisms and cells in tissue culture are now available, new methods are needed for handling solid tissues and, in the case of small-sized animals, whole organisms. Here we describe a simple and rapid method for preparing large DNA molecules from mammalian spleen, whole insects of Drosophila and Planococcus lilacinus, a mealybug. Briefly the method involves gentle steps for preparing cell suspensions and handling of these cells within agarose blocks for preparing the DNA. In mammals like mice, the spleen, rather than the liver, is the organ of choice because, in the latter, endogenous nuclease activity is high
