Yamen was an original plant and a vital zone of the Fatimid mission under the able and loyal headship of Ibn Hawshab. In 291/904, however, his close associate, Ali bin Fazal al-Jadani had shown signs of disloyalty, and in 299/911, he publicly renounced his allegiance to al-Mahdi. It must be noted that in Egypt, when al-Mahdi decided to go to Maghrib instead of Yamen in 291/904, the daiFiruz also gave up Ismaili faith and fled to Yamen, and instigated a revolt. He won the support of Ali bin Fazal. Subsequently, Firuz was killed and Ali bin Fazal endeavoured unsuccessfully to coerce the collaboration of Ibn Hawshab. The death of Ibn Hawshab took place in 303/914, and had made a will to his son Abul Hasan Mansur and his pupil Abdullah bin Abbas al-Shawiri to administer the mission in Yamen till an official appointment of a new chief dai by al-Mahdi. Upon his death, al-Shawiri had sent a letter to al-Mahdi, reporting the death of Ibn Hawshab, and requesting for any chief dai instead. In a reply, al-Mahdi confirmed the post of al-Shawiri as a chief dai. Jafar, the son of Ibn Hawshab was alone among his brothers to demonstrate his loyalty to the Fatimids, but his elder brother, Abul Hasan Mansur, who was expecting to succeed his father, had defected from the mission, and returned to his castles in Miswar, where he was joined by his brothers. Jafar, noticing the inimical intentions of his brothers towards al-Shawiri, tried to persuade that a quarrel would only lead to impair the Ismaili influence in Yamen. In spite of this warning, Abul Hasan Mansur waited for his opportunity, and killed al-Shawiri and took the dominions. Jafar immediately went to Maghrib, where he reached when al-Mahdi had expired in 322/934. Imam al-Qaim charged him the mission work in Maghrib, where he also served Imam al-Mansur and Imam al-Muizz, and was commonly known as Jafar bin Mansur al-Yamen.
It must be known that Ishaq bin Imran, known as Summ Sa'a, a pioneer physician-philosopher had introduced high standard of medical education and practice at the beginning of the Fatimid period. In view of his great ability, intellegiance and independent spirit, he influenced professional development through out Maghrib. His widely known and eloquent student was Abu Yaqub bin Suleman, who managed to become the personal physician of Abu Abdullah and continued his service at the Fatimid court with al-Mahdi, and died in 320/932 at Kairwan. His medical works were among the first to be translated into Latin, the task being accomplished by Constantine the African about 1080. His works exercised much influence on western medieval medicine, and were still being read in the 17th century. Robert Burton (1577-1680) quotes them freely in his "Anatomy of Melancholy." Ibn Suleman's medical works included "al-Hummayat" on fevers, which was translated into Latin and Hebrew in Europe. His another work "Aqawil fi taba'i al-Aghdhiya wal Adwiya" deals on diet and drug. And above all, his treatise on urine dominated medicine for many centuries. Very remarkable is his small tract, extant in Hebrew translation only, called "Guide for Physicians." It shows a high ethical conception of the medical profession.
The medico-pharmaceutical contribution in Maghrib under al-Mahdi reached their highest expression in the works of Abu Jafar bin al- Jazzar (905-984) in Kairwan. He was the student of Ibn Suleman. He used to go to Manastir, a town in Tunisia, where, next to his regular clinic, he erected a cabin as an apothecary shop, wherein he kept his syrups, electuries etc. His chief work, "Provision for the Traveller" was early translated into Latin as the "Viaticum", Greek "Ephodia" and Hebrew.