The role of steroid/thyroid hormones in the regulation of endocrine cells at the level of the pituitary has remained unclear. Therefore, using single-cell quantitative real-time PCR we examined absolute amounts of transcripts for nuclear receptors (estrogen:ER, ER and ER; androgen:ARa and ARb; glucocorticoid:GR1, GR2a and GR2b; thyroid hormone:TR1, TR2 and TR) in pituitary cells of immature (IM) and mature (M) male tilapia, Oreochromis niloticus. In the two reproductive stages, ACTH cells expressed only ER, while all other pituitary cell types expressed ER + and a subpopulation co-expressed ARa, ARb, GR1, GR2b and TR, but lacked ER, GR2a, TR1 and TR2. Immature males had high percentages of LH cells (IM:46.0% vs. M:10.0%), GH cells (IM:23.3% vs. M:7.9%) and prolactin cells (IM:68.8% vs. M:6.0%) with ER; TSH cells (IM:19.2% vs. M:0.0%) and MSH cells (IM:25.6% vs. M:0.0%) with ER+TR. A high percentage of FSH cells in immature males expressed ER (IM:46.9% vs. M:18.8%) and FSH cells in mature males showed significantly high GR1 transcripts (IM:76.0±5.0 vs. M:195.0±10.7 copies/cell, P<0.05), suggesting that FSH cells are regulated differently in the two reproductive stages. Co-expression of ER+ in high percentages of cells of the growth hormone family (GH, IM:43.8% vs. M:14.3%; prolactin, IM:8.3% vs. M:59.7%; somatolactin, IM:22.2% vs. M:42.2%) suggests that the expression of both ERs is important for functionality. Thus, differential co-expression of genes for nuclear receptors in subpopulations of pituitary cell types suggests multiple steroid/thyroid hormone regulatory pathways at the level of the pituitary during the two reproductive stages.