Recent technical advances have rapidly advanced the discovery of novel peptides, as well as the transcripts that encode them, in the parasitic nematode Ascaris suum. Here we report that many of these novel peptides produce profound and varied effects on locomotory behavior and levels of cyclic nucleotides in A. suum. We investigated the effects of 31 endogenous neuropeptides encoded by transcripts afp-1, afp-2, afp-4, afp-6, afp-7, and afp-9 - 14, (afp: Ascaris FMRFamide –like Precursor protein) on cyclic nucleotide levels, body length and locomotory behavior. Worms were induced to generate anteriorly propagating waveforms, peptides were injected into the pseudocoelomic cavity, and changes in the specific activity (nmol/mg protein) of second messengers cAMP (3′5′ cyclic adenosine monophosphate) and cGMP (3′5′ cyclic guanosine monophosphate) were determined. Many of these neuropeptides changed the levels of cAMP (both increases and decreases were found), whereas few neuropeptides changed the level of cGMP. A subset of the peptides that lowered cAMP was investigated for effects on the locomotory waveform and on body length. Injection of AF19, or AF34 (afp-13), AF9 (afp-14), AF26 or AF41 (afp-11) caused immediate paralysis and cessation of propagating body waveforms. These neuropeptides also significantly increased body length. In contrast, injection of AF15 (afp-9) reduced the body length, and decreased the amplitude of waves in the body waveform. AF30 (afp-10) produced worms with tight ventral coils. Although injection of neuropeptides encoded by afp-1 (AF3, AF4, AF10 or AF13) produced an increased number of exaggerated body waves, there were no effects on either cAMP or cGMP. By injecting peptides into behaving A. suum, we have provided an initial screen of the effects of novel peptides on several behavioral and biochemical parameters.