From the rhizomes of Nuphar lutea four new alkaloids were isolated. Their structures were established as syn-6-hydroxythiobinupharidine sulphoxide, syn-6′-hydroxythiobinupharidine sulphoxide, syn-6,6′-dihydroxy thiobinupharidine sulphoxide and anti-thiobinupharidine sulphoxide. © 1986.