Composition of nutrient media, flower bud size, sucrose concentration, heat shock stress, and ethylene inhibitor could have marked effects on microspore embryogenesis. No microspore-derived embryos (MDE) were formed when the microspores were isolated from radish (Raphanus sativus L.) flower buds of 1.0-2.5 mm in size, whereas MDE were formed with microspores isolated from 2.5-4.5 and 4.5-6.5 mm flower buds. The microspores isolated from 2.5-4.5 mm flower buds showed high embryo yields. MDE formation was highest when $150g{cdot}L^{-1}$ sucrose was added to the half strength Nitsch & Nitsch (NLN) liquid medium, but at sucrose concentrations less than $100g{cdot}L^{-1}$ there was no MDE formation. Microspores cultured on half strength NLN liquid medium containing $0.05mg{cdot}L^{-1}$ silver nitrate ($AgNO_3$) produced the most MDE, showing more than two-fold increase in yield compared to those cultured on medium without $AgNO_3$. A heat shock pretreatment of microspores at $32^{circ}C$ for 24 h gave high-frequency production of MDE when compare to higher or lower temperatures; no MDE were formed at $42.5^{circ}C$. The highest yield of MDE was observed when microspores were derived from 2.5-4.5 mm flower buds cultured on half strength NLN medium containing $150g{cdot}L^{-1}$ sucrose, $0.05mg{cdot}L^{-1}$ $AgNO_3$, and precultured with heat shock pretreatment of microspores at $32^{circ}C$ for 24 h, followed by incubation $25^{circ}C$ for 30 days. A polyploidy test indicated that 19.7% of the microspore-derived plants were doubled haploid, other plants were haploid, and chimeras were haploid and diploid.