Haptoglobin and transferrin (TF) types were determined for 134 patients with leukaemia of the four most common types: acute lymphocytic (ALL), chronic lymphocytic (CLL), acute myelocytic (AML) and chronic myelocytic leukaemia (CML). The phenotype HP1 was found to have an increased incidence in the total patient group due to an increased incidence in those with AML, ALL and CML compared with controls, but not in those with CLL. Although tests of association applied to each of the samples of the four common types of leukaemia produced no significant chi 2 values, they did indicate that the relative incidence (RI) was just under 2 for the groupings of the acute forms ALL and AML, the myelocytic forms AML and CML and for the combination of ALL, AML and CML, respectively. All these associations were statistically significant (p less than 0.05). Analysis of TF subtypes and leukaemia indicated a significantly increased frequency of TF C1C1 among leukaemia patients compared with controls (p less than 0.005). Analysis of the samples of each of the four common types suggested that while the RI was raised in all but ALL patients, the association was significant only in AML patients (p less than 0.05). However, when the two myelocytic types were combined the RI was 2.3 and the association was highly significant (p less than 0.005). No such association could be detected in the lymphocytic forms.