By observing isolated long DNA chains with fluorescence microscopy, the collapsing transition of individual single DNAs induced by polyethylene glycol with pendant amino groups (PEG-A) was compared to that induced by neutral polyethylene glycol (PEG). The main results are as follows : (1)DNA is collapsed by PEG-A at concentrations 10(5) times lower than those required for PEG. (2) In PEG-A, the concentration which induces collapse decreases with an increase in the salt concentration. This trend is similar to that in the collapse induced by PEG. (3) The transition induced by PEG is all-or-none; individual DNA chains exhibit either elongated coil or compacted globule states. On the other hand, segregation of a collapsed region along a single DNA chain occurs as an intermediate state in the collapsing transition induced by PEG-A.