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The hyperfine resolved rotational spectrum of the CH[sub 2]CP radical in the &Xtilde;²B[sub 1] ground electronic state has been observed for the first time using a Fourier transform microwave spectrometer in combination with a pulsed discharge nozzle. The radical was produced by discharging a mixture of PH[sub 3] and C[sub 2]H[sub 2] diluted in either Ar or Ne. A total of 25 hyperfine components of the 2[sub 02]-1[sub 01] and 3[sub 03]-2[sub 02] transitions have been measured which enabled us to precisely determine hyperfine coupling constants for both phosphorus and hydrogen nuclei. Spin densities on the phosphorus and β-carbon atoms, estimated from the hyperfine coupling constants, suggest that the radical forms an allenic structure (CP double bond) that is modified by a phosphoryl structure (CP triple bond), which is consistent with the theoretical estimation obtained previously by an ab initio calculation. The nature of the CP chemical bond in the radical is investigated in comparison with the corresponding nitrogen bearing counterparts. [ABSTRACT FROM AUTHOR]