The possibility that the peanut agglutinin (PNA) receptor and/or its co-ordinate structures on the surface of leukaemia cells might be recognized by lectin free crude interleukin-2 (IL-2) activated human peripheral blood lymphocytes (LAK) was investigated. Analysis was undertaken of the correlation between the sensitivity to allogeneic LAK lysis and the proportion of PNA receptor on different fresh malignant cells. The results obtained suggested that PNA receptor detected by rhodamine isothiocyanate labelled PNA binding assay appeared to be well expressed on leukaemia cells which were sensitive targets for LAK. PNA receptor and/or its coordinate structures seemed to provide a 'target' structure for LAK.