Chediak-Higashi Syndrome (CHS) has been associated with recurrent bacterial infections and defective polymorphonuclear (PMN) leukocyte function. Confirmation of the diagnosis of CHS and defective PMN function was established in a 2-month-old with accelerated phase CHS. The diagnosis was confirmed by demonstrating reduced PMN degranulation (beta-glucuronidase release 34.1 +/- 0.9% versus 5.1 +/- 4% and lysozyme release 17.6 +/- 1.2% versus 11.1 +/- 7% (control versus CHS) and staphylococcal bacterial killing at 15' 51.4 +/- 3.6% versus 24.9 +/- .4% (control versus CHS). Additional studies using fluorescent cytometric analysis were made to investigate other etiologies of PMN dysfunction in CHS. Total cell density and PMN granularity, as measured by fluorescent-activated cell sorter side scatter analysis, was no different from CHS and age-matched controls. Although CHS is characterized by large PMN granular inclusions, right angle light scatter analysis in this study suggests that the total cell density within the PMN of patients with CHS is normal (D less than .01). PMN granular release of surface receptors was also studied using antibody binding and fluorescent analysis. OKM1 antibody-binding demonstrated significantly reduced C3bi (MO-1) receptor expression (13% of control) p less than 0.001. Decreased surface reception expression of C3bi receptors may play an additional role in defective PMN mobility, chemotaxis, and bactericidal activity in patients with CHS.