The pyroelectric effects of dipolar guest molecules in molecular sieve crystals have been studied for the first time. The measurements have been done on assemblages of aligned crystals as well as on individual single crystals of the aluminophosphate molecular sieve AlPO4-5 loaded with p-nitroaniline (PNA). The PNA molecules form unidirectionally aligned dipole chains in parallel molecular sieve channels. We found that the PNA dipoles are oppositely directed in the two halves of a single crystal, forming two macroscopic regions of opposite polarization. It is concluded that the preferred direction of the dipole chains in the channel is a result of the adsorption process of the molecules into the channels.