<p>This paper, based upon research financed by the Inland Revenue and the Contributions Agency of the DSS, presents calculations of the compliance costs for employers of PAYE and National Insurance in 1995-96. Total costs are estimated to have been of the order of £1.3 billion. The costs are very unequally spread across employers, whether measured per employee or per pound of tax raised. They are particularly high for small new employers. For the largest employers, these costs may be offset by the cash-flow benefits of acting as tax collectors. The composition of labour and other costs is calculated and estimates are made of compliance costs under various payroll 'technologies'. The main determinants of compliance costs, for an employer, are analysed using weighted least-squares regression analysis. Finally, some policy implications are considered. </p>