The presence of steroids in larval and mature brook lampreys (Lampetra planeri Bloch).

The presence of steroids was investigated by radioimmunoassay - mass spectrometry in serum and homogenates of gonads and presumed adrenocortical (pro- and opisthonephric) tissue of larval and mature brook lampreys (Lampetra planeri Bloch) of both sexes. Pregnenolone was detected in all tissue samples studied whereas androstenedione could be identified only in presumed adrenocortical tissue from male and female mature animals as well as in testis. Testosterone was present in testis of adult lampreys and in sera of larval and adult animals.