<jats:p><jats:bold>Antibiotics from Gliding Bacteria, XXXVI. – A New Isoquinoline Alkaloid from <jats:italic>Myxococcus xanthus</jats:italic></jats:bold><jats:p>From the culture broth of <jats:italic>Myxococcus xanthus</jats:italic> Mx ×48 we have isolated the 5,8‐dihydroxy‐4,7‐dimethoxy‐2,6‐dimethylisoquinolinium formate (<jats:bold>4</jats:bold>); To confirm the structure of <jats:bold>4</jats:bold> we compared its spectroscopic properties with 5‐hydroxy‐2‐methylisoquinolinium methylsulfate (<jats:bold>5</jats:bold>).