In a 56-year-old male patient, receiving chemotherapy after radical surgery for bladder carcinoma, an unusual type of cytoplasmic inclusion was discovered in about 30% of peripheral blood lymphocytes. This was a single, large (about 2 microns in diameter), round or ovoid body, darker than the nucleus and reddish-violet in May-Grünwald-Giemsa stain. The examination with transmission electron microscope demonstrated that such inclusions were made up of giant parallel tube arrays (PTAs). The absolute lymphocyte count was normal, but there was an expansion of CD3+, CD4-, CD8+, CD11b, TCR alpha beta lymphocytes. The lymphocytes bearing the inclusion were CD3+ and CD8+. DNA studies suggested an expansion of T-cell population with clonal rearrangement of TCR beta and TCR gamma. This case can be classified as an asymptomatic disorder of large granular lymphocytes, with unusual morphology. Giant PTAs should be taken into account in the differential diagnosis of lymphocyte cytoplasmic inclusions.