As first observed in chick embryos (Lewis, 1924), prenatal airways exhibit spontaneous phasic contractility immediately ex vivo and in vitro.Agonists e.g. acetylcholine and K⁺ depolarising solution augment contractions (Sparrow et al. 1994) whereas calcium antagonists e.g. nifedipine reduce or even abolish narrowing of the airways (McCray 1993). We therefore postulate Ca²⁺ influx underlies spontaneous contractility of prenatal airway smooth muscle. This study tests the above hypothesis. Embryonic lungs (n=10) were microdissected on day 13.5 of gestation (term = day 21) from time-mated Sprague-Dawley rats that were killed humanely. Lungs were cultured at 37°C in 5% CO₂ and passively loaded with two calcium-sensitive indicators after 54 and 78 hours. Indo-1 was utilised for photometric measurements of [Ca²⁺]_i and Fluo-4 for Confocal imaging. For each lung primordia Ca²⁺ transients were observed for at least 30 minutes at 22°C and 30°C. Relaxation half-times (T₅₀) of the calcium transient were determined from at least four representative spikes and are expressed as means ± SE.Ca²⁺ waves propagated at 220-420µm/sec longitudinally through the embryonic bronchi and consistently preceded airway contraction. Both techniques (photometric and confocal) yielded Ca²⁺ transients with similar temporal characteristics. Ca2+ transients feature an initial fast phase (amplitude = 70% of peak), a second slow phase (attainment of peak), followed by a plateau phase at peak. Only the slow and plateau phases were prolonged at 22°C compared to 30°C. Relaxation half-time (T₅₀) of the Ca²⁺ transient was 8.29 ± 1.89 seconds at 22°C and 4.40 ± 0.73 seconds at 30°C. Ca²⁺ oscillations occur every 60 seconds at room temperature, every 30-40 seconds at 30°C, and were potentiated by Ca²⁺ agonist Bay-K 8644 (1µM) and inhibited by nifedipine, (10µM). We have shown for the first time propagation of Ca²⁺ transients mediate embryonic airway contractility via L-type Ca²⁺ channel dependent calcium influx.