Respiration rates of developing muskmelon (Cucumis melo L.) seeds were determined polarographically using a Clark-type O₂ electrode (Hansatech LD2). Seeds were obtained from fruits harvested 20, 30, 40, and 50 days after anthesis (DAA). Respiration (O₂ uptake) was measured for fresh intact seeds and fresh dissected seeds. The respiration rate of intact seeds declined from a maximum of 2.28 μmol O₂/min/g DWT at 20 DAA to a minimum of 0.16 μmol O₂/min/g DWT at 50 DAA. Dissecting intact seeds into embryo, testae, and perisperm tissues increased the respiration rate of 20 DAA seeds to 3.12 μmol O₂/min/g DWT but had no effect on more mature seeds. Respiration rate was highly correlated with seed relative growth rate and water content. Respiration rate was not consistently changed after incubation in water. This indicates that respiration rate is not directly controlled by subtle variations in water content. Rather, seed respiration rate is directly linked with turgor-driven, expansive growth and relative growth rate. Fifty-DAA seeds from dry storage were imbibed on water saturated blotters, and respiration rates of whole seeds, decoated seeds, and embryos were compared. Respiration during imbibition was not significantly inhibited by the testae or perisperm tissue. In addition, 50-DAA dried, imbibed seeds were subjected to reduced O₂ concentrations ranging from 3.5 kPa partial pressure O₂ (pO₂) to 21 kPa pO₂. Respiration was not limited by O₂ until pO₂ was reduced to approximately 5 kPa, indicating a high affinity for O₂. Gas chromatography revealed that pO₂ in the seed cavity of muskmelon fruits ranged from 12.5 to 8 kPa. Fifty-DAA seeds from dry storage were imbibed on polyethylene glycol (PEG), mannitol, or NaCl ranging from -0.5 to -2.5 MPa water-potential or on abscisic acid (ABA) solutions ranging in concentration from 10 to 50 μM. Respiration and solution water-potential were measured at 10-hr intervals. At 10 hr of imbibition, each type of osmoticum and ABA stimulated respiration to values greater than for seeds imbibed in pure water. Beyond 10 hr, respiration rates were variable.