SUMMARYMorphological evidence of activation in vivo of circulating neulrophils in patienis with inflammatory bowel disease (IBD) was sought by quanlilative light microscope examination of toluidlne biuestained leucocyte preparations made from peripheral venous bloods thai had been fixed immediately ex vivo. The proportion of spherical (unactivated) circulating neulrophils was reduced in active Crohn's disease (73%; 46 96 (median; range),/i= 11) compared with inactive Crohn's (90%; 45 99; /i=18. P<00\) and nornial subjects (94%; 44-98; n=13, P<005}. There tended to be fewer spherical neutrophils in active ulceralive colitis {71'V..; 1^-96, ti= 17) than in quiescent colitis (88%; 57-99. H^ 13, /'<()• 1) or normal subjects (P<005). Activated neutrophils occur in the circulating pool of palients with active IBD and can be detected by light microseopy of peripheral venous blood leucocyte preparations.