Chronic mucoid infections are a major scourge in cystic fibrosis patients. Mucoid displays structured alginate-rich biofilms that are resistant to antibiotics. Here, we have assessed the efficacy of a panel of alginate lyases in combating mucoid biofilms in cystic fibrosis. Albeit we could not demonstrate alginate degradation by alginate lyases in sputum, we demonstrate that the endotypic alginate lyases, Aly (from ) and AlyVI (from sp. QY101) and the exotypic alginate lyases, AlyFRB (from sp. alg1), and SA1-IV (from sp. A1), indeed inhibit biofilm formation by a mucoid strain isolated from the sputum of a cystic fibrosis patient with comparative effect to that of the glycoside hydrolase PslG, a promising candidate for biofilm treatment. We believe that these enzymes should be explored for in vivo efficacy in future studies.