Vertebrate haematopoiesis relies on a pool of haemetopoietic stem/progenitor cells (HSPCs) that can self-renew and differentiate into all haematopoietic lineages. But what are the molecular mechanisms that regulate this process? Here, Zilong Wen and co-workers (p. 619) identify two novel factors that regulate zebrafish HSPC maintenance. During zebrafish development, HSPCs originate from the ventral wall of the dorsal aorta (VDA), migrate to the caudal haematopoietic tissue (CHT) and finally colonise the kidney. The researchers isolated and characterised two haematopoiesis-deficient mutants, rumbahkz1 and sambahkz2. In these mutants, HSPC specification in the VDA and subsequent homing to the CHT are normal, but further HSPC development within the CHT is compromised. Using positional cloning, they show that Rumba is a novel nuclear C2H2 zinc-finger protein and that samba encodes a protein that is homologous to human augmin complex subunit 3 (Haus3). Both factors, they report, act independently and cell-autonomously to regulate cell cycle progression in HSPCs, and thus are essential regulators of zebrafish haematopoiesis.