Lichenoid tissue reaction (LTR) is characterised by epidermal basal cell damage which takes the form of liquefaction degeneration or cell death either apoptosis or necrosis with an associated cascade of histologic events in epidermis and dermis. LTR is found in clinical conditions with lichenoid poikilodermatous and pigmentary dermatoses. A selected group of fifty lichenoid and pigmentary dermatoses such as Lichen planus (LP) Discoid lupus erythematosus (DLE) Lichenoid melanodermatitis (LM) and Lichen nitidus (LN) were studied. In LP basal cell liquefaction degeneration was extensive in comparison to other disease with large number of Civatte bodies and colloid bodies. There were significant vasodilatation in upper dermis inside the massive band like infiltrate. PAS positive basement membrane was disrupted in reaction area. Hypergranulosis was conspicuous. Chronic DLE showed spotty lichenoid reaction in the form of basal cell liquefaction degeneration. Civatte bodies and colloid bodies were infrequent. Infiltrate was more focal but could be band like. Epidermal atrophy and thickening of PAS positive basement membrane were important differentiating features, LM or Melanodermatitis toxica revealed focal mild to moderate liquefaction degeneration of basal cells with atrophy of the epidermis. The infiltrate although band like was less dense with marked pigmentary incontinence in clumps and giant melanophages. Civatte bodies, colloid bodies were not found and vascular changes were less prominent. LN showed localised basal cell damage with claw like rete ridges clutching a dense infiltrate. The dermal infiltrate often showed multinucleated giant cell. Civatte bodies and colloid bodies were not present. In some cases of the overlap syndrome LP/LE a careful study of lichenoid tissue reaction could distinguish these two diseases.(ABSTRACT TRUNCATED AT 250 WORDS)