Some IRAS LRS sources can not be identified in the
 optical POSS charts and even were not detected in near-infrared.
 They are peculiar objects in that the very sharp change of energy
 distribution happens between 12 micron and
 near-infrared. Both the brightness at far infrared and invisibilty
 at optical band indicate a cold and thick circumstellar envelopes.
 So such objects without near-infrared detection proposes one
 question that why the thick circumstellar envelopes do
 not
 emit much in the near-infrared, i.e. K band magnitude fainter
 than 10 or flux density weaker than 0.067 Jy at 2.2 micron.
 The mystery can be caused by two factors. One is that
 the circumstellar envelopes contain some special dust
 components which absorb much between 12 micron and 2 micron or
 emit much in the far-infrared.  The other is that the
 sources are not point-like but extended. The non-detection at
 K band is caused by the smaller diaphragm compared with IRAS
 diaphragm. Since optical and near-infrared observation can
 not provide any information about them at present
 on the ground, ISO will be the only way to study them in mid- and
 far-infrared from space. Furthermore, they are IRAS bright
 which make them very appropriate for ISO detection. These very
 few sources stand for a peculiar group and may be in a
 special evolutionary stage between AGB star and planetary
 nebula.