The aim of this study is to determine whether, in situations of marked immunological deficit, principally among patients with AIDS, there is a greater frequency of protozoal forms. Comparative study was of 2 group of patients, 1 an immunocompromized group, main HIV+, and the other a non-immunocompromized group with different respiratory disorders (control group). A cytological study was carried out using 295 sputum smears, obtained between 1994 and 2003, from patients at the Central University Hospital of Asturias, Spain. Smears were valid for 106 patients, 83 of whom presented HIV infection. Protozoa were detected in 72 of this group. Our findings indicate a greater number of protozoal forms in the sputa of patients with AIDS than among the other 2 groups analysed (patients without AIDS and control group).