Lentinan is a beta 1-->3 glucan isolated from Lentinus edodes (Shiitake mushroom) which has immune modulating properties. We have conducted two phase I/II placebo-controlled trials on a total of 98 patients. In one study at the San Francisco General Hospital (SFGH), ten patients each were administered 2, 5, or 10 mg of lentinan or placebo i.v. once a week for eight weeks. In the second study at the Community Research Initiative in New York (CRI), two groups of 20 patients each were administered 1 or 5 mg of lentinan i.v. twice a week for 12 weeks, and ten patients were administered placebo (vehicle containing mannitol plus dextran 40) i.v. twice a week. Entry criteria were an HIV positive test, CD4 levels of 200-500 cells, age 18-60 years, and without current opportunistic infections. This study confirms, in Caucasian subjects also, the good tolerability of lentinan observed in Japanese cancer patients. Side effects were mainly mild, especially when infusion was carried out over a 30-minute period. In the SFGH study, where administration was over a ten minute period, there were nine side effects severe enough to be reported to the FDA (one case each of anaphylactoid reaction, back pain, leg pain, depression, rigor, fever, chills, granulocytopenia and elevated liver enzymes) and there were four patients who discontinued therapy because of side effects. In the CRI study, where infusion was over a 30-minute period, there were no side effects reportable to the FDA and there were four dropouts due to side effects or personal preference. Most side effects resolved promptly after the discontinuation of medication, and all of them were relieved within 24 hours. Patients in the study have shown a trend toward increases in CD4 cells and in some patients neutrophil activity. Because of the small numbers, these values do not have statistical significance. Inasmuch as no side effects such as anemia, leukopenia, pancreatitis or neuropathy were seen, and in view of the positive effects of lentinan on certain surrogate markers (recognizing that these were small studies), we recommended a long-term clinical trial of lentinan in combination with didanosine (ddI) or zidovudine in HIV positive patients. Most patients in these trials did not have measurable p24 levels. In the CRI trials of ten patients with elevated p24 levels, eight on lentinan and two on placebo had decreased p24 levels. Of these decreases, those with lentinan and one with placebo were marked. These results were provocative and needed confirmation. Subsequent to this study, a trial of lentinan in combination with didanosine (ddI) showed a mean increase of 142 CD4 cells/mm3 over a twelve month period, in contrast to a decrease in CD4 cells in patients on ddI alone (Gordon et al. 1995).