Some authors have shown that lysine acetylsalicylate (LAS) may help prevent nasal polyp relapses. As some anti-inflammatory drugs have been found to regulate cell growth, we investigated the antiproliferative effect of LAS on fibroblasts derived from nasal polyps. Moreover, we studied the effect of LAS on the growth of fibroblasts derived from normal skin to determine whether the response was similar to that obtained in the above-mentioned cells. Fibroblasts were obtaitied from tissue samples of nasal polyps from two aspirin-tolerant and two aspirin-intolerant patients, and from the normal skin of a healthy donor. The cells were treated with LAS (20–2000 μg/ml of culture medium). Cell growth and viability were evaluated after 3 and 6 days of culture. LAS had a growth-inhibitory effect on cells independently of their derivation. A reduction in cell growth was seen at the coticentrations of LAS tested, which correspond to those used in the local treatment of nasal polyposis.