The plerocercoids of all Spirometra forms investigated up to now in this regard produce a "Sparganum Growth Factor" (SGF), i.e. one (or more) substance(s) with growth hormone-like effect on certain rodents. The SGF produced by the species S. mansonoides (SGF "mansonoides") is stronger effect than the SGF produced by all the other forms (SGF "non-mansonoides"). The physiological in its effects hitherto investigated mainly with SGT "mansonoides" in the USA are shortly mentioned. In order to get further insights the isolation, purification, and characterization of the SGF are necessary. The both kinds of SGF are also of taxonomic importance.