Narrowly distributed spherical poly(N-vinylcaprolactam) (PNVC) microgels were prepared by precipitation polymerization in water. The effect of both anionic (sodium dodecyl sulfate, SDS) and cationic (N-dodecylpyridinium bromide, DPB) surfactants on the swelling and shrinking of the microgels were investigated by laser light scattering (LLS). Our results showed that the microgels gradually shrank to the collapsed state when the temperature increased from 20 to similar to 38 degrees C. The addition of anionic surfactant caused an extra swelling of the microgels and shifted the collapsing temperature higher, whereas the addition of cationic surfactant has different effects on the swelling and shrinking of the microgels prepared by using different initiators, depending on whether the decomposed fragments of the initiator are ionic or neutral. Our results clearly showed that the ionic groups introduced into polymer gels from the initiators should be taken into consideration in the study of the surfactant/gel interaction.