We used thin-film differential scanning calorimetry to investigate the melting of isolated polyethylene single crystals with lamellar thicknesses of 12 +/- 1 nm. We observed the melting of as few as 25 crystals. Over a wide number of crystals (25-2000 crystals), the heat of fusion was 40% larger than the bulk value. The melting temperature of the isolated single crystals was 123 +/- 2 degreesC, 9 degreesC lower than that of the bulk material. We also measured the heat of fusion of quenched crystals (+/- 15%) over a wide range of heating rates (20,000 -100,000 K/s). Annealing the quenched crystals resulted in shifts in the endotherm peak by as much as 15 degreesC.