(+)-α(S)-Butyramido-γ-butyrolactone is a minor constituent of the toxic marine blue-green alga Lyngbya majuscula. Lyngbya majuscula is a toxic marine cyanophyte that is responsible for occasional outbreaks of a contact dermatitis known as 'swimmers' itch'. The toxin associated with the dermatitis-producing strain is debromoaplysiatoxin [1], but whether this compound actually causes the dermatitis is not known for certain. The toxin associated with the non-dermatitis-producing variety is a different substance [2]. In an investigation of this latter toxin, we have isolated a minor constituent of the alga and have identified it as (+)-α(S)-butyramido-γ-butyrolactone (1). The lactone was found in the gel filtration fraction that was eluted immediately after the toxin. Its structure was determined in a straightforward manner from spectral data (see Experimental) and confirmed by acid hydrolysis to n-butyric acid and α-amino-γ-butyrolactone and synthesis from (-)-α(S)-amino-γ-butyrolactone and butyryl chloride. (+)-2(S)-N-Acetamido-3(R)-acetoxyoctadecan-1-ol, a diacetate of dihydrosphingosine, and fatty acid amides of (-)-2(S)-amino-3(R)-hydroxyoctadec-4(E)-en-1-ol (sphingosine) have been isolated from extracts of Hawaiian Laurencia nidifica and Amansia glomerata, respectively. Although well known as constituents of nerve tissue hydrolyzates throughout the animal kingdom, these compounds have not been previously found in plants.