Treatment of mice with 200 and 800?mg/kg Ferroquine, shows low total worm burden reductions of 19.4% and 35.6%. One of the mice treated with 800?mg/kg Ferroquine died within 24?hours post-treatment. No activity is observed treating mice with RQ at 200?mg/kg. Finally, a total worm burden reduction of 17.3% is observed following treatment with FQ-OH. Hence, modification of Chloroquine (CQ) by a ferrocenyl or ruthenocenyl fragment does not increase the antischistosomal properties of CQ. For comparison, at 200?mg/kg mefloquine (MQ) achieves a much higher worm burden reduction of 72.3% in S. mansoni-infected mice. A higher effect against female adult S. mansoni is also observed in MQ treated mice pointing to a sex-specific interference of these drugs with the target. Furthermore, in one of the FQ-OH treated mice many dead worms are recovered and a hepatic shift (i.e. worms migrating to the liver) observed. Hence, Ferroquine and FQ-OH show weak antischistosomal activity in vivo^[1].