Peripherally harvested lymphocytes have been labelled with 51Cr, reinjected into human subjects and their distribution then studied. Evidence is presented which suggests faecal loss of 51Cr represents loss of T lymphocytes and that there is normally a pathway of lymphocyte removal into the gut of probable importance in lymphocyte migration streams. In 9 normal subjects, without structural intestinal disease, faecal loss of lymphocytes over 5 days was 0.20 % (SEM ± 0.06) whereas in 5 patients with untreated coeliac disease faecal loss was 1.13 ± 0.34 %, in 7 with Crohn’s disease it was 1.01 ± 0.21 % and in 5 with intestinal lymphangiectasia loss was 0.61 ± 0.10%. In 1 patient with acute tropical sprue, enteric loss was 0.97 %. By contrast, faecal loss was normal in 3 coeliac patients in remission on a gluten-free diet. Measurements were also made using an external counter. In contrast to the normals, where count rates steadily diminished, an increasing activity was recorded over the umbilicus over 7 days after dose administration in all the disease categories studied with the exception of the treated coeliacs. The finding of an increased enteric loss of lymphocytes may explain many of the immunological abnormalities in the conditions studied.